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1. Shard Calculation

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Response:

Calculated Shard: 92 (from laksa043)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa092.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor\')), getAhrefsUnparsedNoserviceFromURL(\'https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor","crawl_time":1775340976,"first_indexed_time":1507912924,"http_code":200,"src_unparsed":"com,wikihow!www,\/Calculate-Voltage-Across-a-Resistor s443","src_root_hash":"12431216878206919092","history_drop_reason":null,"meta_title":"How to Calculate Voltage Across a Resistor (with Pictures)","meta_descriptions":["Before you can calculate the voltage across a resistor, you'll first have to determine what kind of circuit you are using. If you need a review of the basic terms or a little help understanding circuits, start with the first section...."],"attrs_boilerpipe_text":"Download Article\nDownload Article\nBefore you can calculate the voltage across a resistor, you'll first have to determine what kind of circuit you are using. If you need a review of the basic terms or a little help understanding\ncircuits\n, start with the first section. Otherwise, jump ahead to the type of circuit you have to solve.\nLet’s think about current by using an analogy: imagine you pour a bag of corn kernels into a bowl. Each corn kernel is an\nelectron\n, and the stream of kernels flowing into the bowl is the current.\n[1]\nWhen talking about the flow, you describe it by saying how many kernels are flowing each second. When talking about a current, you measure it in\namperes\n(\namps\n), or a certain (very large) number of electrons flowing per second.\nElectrons have a \"negative\" electrical charge. This means they attract (or flow toward) objects with a positive charge, and repel (or flow away from) objects with a negative charge. Since they're all negative, electrons are always trying to push away from other electrons, spreading out wherever they can.\n[2]\nAdvertisement\nVoltage\nmeasures the difference in electrical charge between two points.\n[3]\nThe greater the difference, the more energetically the two sides attract each other. Here's an example with an everyday battery:\nInside a battery, chemical reactions happen that produces a buildup of electrons. The electrons go to the negative end, while the positive end stays mostly empty. (These are called the negative and positive terminals.) The longer this goes on, the larger the voltage between the two ends.\nWhen you connect a wire between the negative and positive ends, the electrons at the negative end suddenly have somewhere to go. They shoot toward the positive end, creating a current. The larger the voltage, the more electrons move to the positive end each second.\nResistance\nis exactly what it sounds like. The more resistance something has, the harder it is for the electrons to push through. This slows the current, since fewer electrons can push through each second.\n[4]\nA resistor is anything in the circuit that adds resistance. You can buy an actual \"resistor\" at an electronics store, but in a circuits problem it might represent a light bulb or anything else with resistance.\nThere's a very simple relationship between current, voltage, and resistance.\n[5]\nWrite this down or\nmemorize\nit; you'll use it often when solving circuit problems:\n[6]\nCurrent = voltage divided by resistance\nThis is usually written: I =\nV\n\/\nR\nThink about what happens when you increase V (voltage) or R (resistance). Does this match what you learned in the explanations above?\nAdvertisement\nA\nseries circuit\nis easy to identify. It's just one loop of wire, with everything arranged in a row. The current flows around the entire loop, going through each resistor or element in order.\nThe\ncurrent\nis always the same at any point along the circuit.\n[7]\nWhen calculating voltage, it doesn't matter where the resistor is on the circuit. You can pick up the resistors and move them around, and you'll still have the same voltage across each one.\nWe'll use an example circuit with three resistors in series: R\n1\n, R\n2\n, and R\n3\n. This is powered by a 12 volt battery. We'll find the voltage across each one.\nAdd together all resistance values on the circuit. The answer is the total resistance of the series circuit.\nFor example, the three resistors R\n1\n, R\n2\n, and R\n3\nhave resistances of\n2 Ω (ohms), 3 Ω, and 5 Ω\nrespectively. The total resistance is 2 + 3 + 5 = 10 ohms.\nUse Ohm's Law to find the current of the entire circuit. Remember, the current is the same anywhere on a series circuit. Once we calculate the current this way, we can use it for all our calculations.\n[8]\nOhm's Law says that the current I =\nV\n\/\nR\n. The voltage across the whole circuit is 12 volts, and the total resistance is 10 ohms. The answer is I =\n12\n\/\n10\n=\n1.2 amperes\n.\nWith basic\nalgebra\n, we can change Ohm's Law to solve for voltage instead of current:\n[9]\nI =\nV\n\/\nR\nIR =\nV\nR \/\nR\nIR = V\nV = IR\nWe know the resistance, we know the current, and we have our equation.\n[10]\nPlug in the numbers and solve. Here's our example problem solved for all three resistors:\nVoltage across R\n1\n= V\n1\n= (\n1.2A\n)(\n2Ω\n) = 2.4 volts.\nVoltage across R\n2\n= V\n2\n= (\n1.2A\n)(\n3Ω\n) = 3.6 volts.\nVoltage across R\n3\n= V\n3\n= (\n1.2A\n)(\n5Ω\n) = 6.0 volts.\nIn a series circuit, the sum of all your answers must equal the total voltage. Add up every voltage you calculated and see if you get the voltage of the entire circuit.\n[11]\nIf you didn't, go back and check for mistakes.\nIn our example, 2.4 + 3.6 + 6.0 = 12 volts, the voltage across the whole circuit.\nIf your answer is slightly off (for instance, 11.97 instead of 12), you probably rounded a number at some point. Your answer is still correct.\nRemember, voltage measures the differences in charge, or numbers of electrons. Imagine counting the number of new electrons you see as you travel along the circuit. If you count them correctly, you're going to end up with the total change in electrons from the beginning to the end.\nAdvertisement\nImagine a wire leaving one end of a battery, then splitting into two separate wires. These two wires run\nparallel\nto each other, then join up again before they reach the other end of the battery. If there's a resistor on the left wire and a resistor on the right wire, those two resistors are connected \"in parallel.\"\n[12]\nYou can have any number of wires in a parallel circuit. These instructions will still work for a circuit that splits into one hundred wires and comes back together.\nIn a parallel circuit, the current flows across each path available to it. Current will flow through the wire on the left, cross the left resistor, and reach the other end. At the same time, current will flow through the wire on the right, cross the right resistor, and reach the end. No part of the current doubles back or flows through two parallel resistors.\nIf you know the voltage across the whole circuit, the answer is surprisingly easy. Each parallel wire has the same voltage as the entire circuit.\n[13]\nLet's say a circuit with two parallel resistors is powered by a 6 volt battery. The voltage across the left resistor is 6 volts, and the voltage across the right resistor is 6 volts. It doesn't even matter how much resistance there is. To understand why, think back to the series circuits described above:\nRemember that adding voltage drops in a series circuit always results in the total voltage across the circuit.\nThink of each path the current takes as a series circuit. The same holds true for this: if you count up all the voltage drops, you'll end up with the total voltage.\nSince the current through each of the two wires only passes through one resistor, the voltage across that resistor must equal the total voltage.\nIf the problem doesn't tell you what the total voltage of the circuit is, you'll need to complete a few more steps. Start by finding the total current passing through the circuit.\n[14]\nIn a\nparallel circuit\n, the total current is equal to the sum of the current running through each parallel path.\n[15]\nIn mathematical terms: I\ntotal\n= I\n1\n+ I\n2\n+ I\n3\n...\nIf you're having trouble understanding this, imagine a water pipe split into two paths. The total amount of water flow is just the amount of water flow in each pipe, added together.\nResistors are not as effective in a parallel circuit, because they only block the current going along one wire. In fact, the more wires there are, the easier it is for the current to find a way through. To find the total resistance, solve for R\ntotal\nin this equation:\n[16]\n1\n\/\nR\ntotal\n=\n1\n\/\nR\n1\n+\n1\n\/\nR\n2\n+\n1\n\/\nR\n3\n...\nFor example, a circuit has a 2 ohm and a 4 ohm resistor in parallel.\n1\n\/\nR\ntotal\n= 1\/2 + 1\/4 = 3\/4 → 1 = (3\/4)R\ntotal\n→ R\ntotal\n= 1\/(3\/4) = 4\/3 = ~1.33 ohms.\nRemember, once we find the total voltage of the circuit, we have found the voltage across any one of the parallel wires. Solve for the whole circuit using Ohm's law.\n[17]\nHere's an example:\nA circuit has 5 amperes of current running through it. The total resistance is 1.33 ohms.\nAccording to Ohm's Law, I = V \/ R, therefore V = IR\nV = (5A)(1.33Ω) = 6.65 volts.\nAdvertisement\nSearch\nAdd New Question\nQuestion\nWhat is the percentage of applied voltage that will be dropped across r3=70 if r1=80 and r2=50?\nCommunity Answer\nIt would be 35%. The higher the resistance, the higher the voltage drop. The ratio of resistances here is 80:50:70. Solving for 70 ohms, we get 35%.\nQuestion\nWhat is the voltage of a 60 ohm resistor if the circuit voltage is 150 volts with two parallel 30 ohm resistors and one 60 ohm resister in the series?\nCommunity Answer\nAssuming you intend to ask what is the voltage drop across the 60 ohm resistor, the answer is 120v. The two parallel 30 ohm resistors have an equivalent resistance of 15 ohms. 1\/(1\/30 + 1\/30) = 15. The total resistance appears as 75 ohms to the 150v source. Find the circuit current by I = E\/R or I = 150\/75 = 2 amps. Find the voltage drop for the 60 ohm resistor with E = I x R or E = 2 x 60 = 120V drop across the 60 Ohm resistor.\nQuestion\nWhat becomes the Voltage if we use 2 resistors of 4W in parallel?\nCommunity Answer\nAs any other data is not provided, the voltage across two resistors of 4w in parallel is the same.\nSee more answers\nAsk a Question\n200 characters left\nInclude your email address to get a message when this question is answered.\nSubmit\nAdvertisement\nVideo\nThe voltage across a resistor is often called a \"voltage drop.\"\nThanks\nIf you have a complicated circuit that involves resistors in series\nand\nresistors in parallel, pick two nearby resistors. Find the total resistance across them using the rules for resistors in parallel or in series, as appropriate. Now you can treat them as a single resistor. Keep doing this until you have a simple circuit with resistors\neither\nin parallel\nor\nin series.\nThanks\nUnderstand the terminology:\nCircuit – composed of elements (e.g. resistors, capacitors, and inductors) connected by wires and wherein current can pass through\nResistors – elements that can reduce or resist current\nCurrent – flow of charge into wires; unit: Ampere, A\nVoltage – work done per unit charge; unit: Voltage, V\nResistance – measurement of the opposition of an element to electric current; unit: Ohm, Ω\nThanks\nThanks for submitting a tip for review!\nAdvertisement\nReferences\nAbout This Article\nArticle Summary\nX\nTo calculate voltage across a resistor in a series circuit, start by adding together all of the resistance values in the circuit. Then, divide the voltage across the circuit by the total resistance to find the current. Once you have the current, calculate voltage for the individual resistors by multiplying the current by the resistance. For example, in a series circuit with 3 resistors of 2, 3 and 5 Ohms, and a voltage of 12 volts, the current would be 12 divided by 10, or 1.2 amperes. For the 2 Ohm resistor, the voltage would be 1.2 times 2, or 2.4 volts.\nIf you want to learn how to calculate voltage in a parallel circuit, keep reading the article!\nDid this summary help you?\nThanks to all authors for creating a page that has been read 1,032,909 times.\nReader Success Stories\nMohd Rodzi Mohamad\nAug 26, 2016\n\"This article is very neatly and clearly explained with illustrations of pictures for better comprehension. 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Mantas Silvanavicius is a Licensed Electrician and the Owner of M+S Electric based in Las Vegas, Nevada. With more than 20 years of experience, he specializes in home electrical installations, testing, and wiring. Mantas and his team have completed projects for companies such as Seiko and Springhill Suites by Marriott. M+S Electric is licensed, bonded, and insured.   \n  \n There are [14 references](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#References) cited in this article, which can be found at the bottom of the page.   \n  \n This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources.   \n  \n This article has been viewed 1,032,909 times.\n\nBefore you can calculate the voltage across a resistor, you'll first have to determine what kind of circuit you are using. If you need a review of the basic terms or a little help understanding [circuits](https:\/\/www.wikihow.com\/Make-a-Simple-Electrical-Circuit \"Make a Simple Electrical Circuit\"), start with the first section. Otherwise, jump ahead to the type of circuit you have to solve.\n## Steps\nPart 1\n\nPart 1 of 3:\n\n### Understanding Circuits\n\n[![PDF download](https:\/\/www.wikihow.com\/extensions\/wikihow\/socialstamp\/images\/icon-pdf.svg) Download Article](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\n1. [![Step 1 Learn about current.](https:\/\/www.wikihow.com\/images\/thumb\/2\/2b\/Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg)\n   1\n   **Learn about current.** Let’s think about current by using an analogy: imagine you pour a bag of corn kernels into a bowl. Each corn kernel is an [electron](https:\/\/www.wikihow.com\/Find-Electrons \"Find Electrons\"), and the stream of kernels flowing into the bowl is the current.[\\[1\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-1) X Research source Serway, R.A. and John W. Jewett, Jr., Physics for Scientists and Engineers with Modern Physics. 8th edition. California: Brooks\/Cole. 2010. Ebook   When talking about the flow, you describe it by saying how many kernels are flowing each second. When talking about a current, you measure it in **amperes** ([amps](https:\/\/www.wikihow.com\/Find-Amps \"Find Amps\")), or a certain (very large) number of electrons flowing per second.\n2. [![Step 2 Think about electrical charge.](https:\/\/www.wikihow.com\/images\/thumb\/a\/a1\/Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg)\n   2\n   **Think about electrical charge.** Electrons have a \"negative\" electrical charge. This means they attract (or flow toward) objects with a positive charge, and repel (or flow away from) objects with a negative charge. Since they're all negative, electrons are always trying to push away from other electrons, spreading out wherever they can.[\\[2\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-2) X Research source\n   Advertisement\n3. [![Step 3 Understand voltage.](https:\/\/www.wikihow.com\/images\/thumb\/7\/79\/Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg)\n   3\n   **Understand voltage.** [Voltage](https:\/\/www.wikihow.com\/Test-Voltage-with-a-Multimeter \"Test Voltage with a Multimeter\") measures the difference in electrical charge between two points.[\\[3\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-3) X Research source     The greater the difference, the more energetically the two sides attract each other. Here's an example with an everyday battery:\n   \n   - Inside a battery, chemical reactions happen that produces a buildup of electrons. The electrons go to the negative end, while the positive end stays mostly empty. (These are called the negative and positive terminals.) The longer this goes on, the larger the voltage between the two ends.\n   - When you connect a wire between the negative and positive ends, the electrons at the negative end suddenly have somewhere to go. They shoot toward the positive end, creating a current. The larger the voltage, the more electrons move to the positive end each second.\n4. [![Step 4 Figure out resistance.](https:\/\/www.wikihow.com\/images\/thumb\/5\/55\/Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg)\n   4\n   **Figure out resistance.** [Resistance](https:\/\/www.wikihow.com\/Measure-Resistance \"Measure Resistance\") is exactly what it sounds like. The more resistance something has, the harder it is for the electrons to push through. This slows the current, since fewer electrons can push through each second.[\\[4\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-4) X Research source\n   \n   - A resistor is anything in the circuit that adds resistance. You can buy an actual \"resistor\" at an electronics store, but in a circuits problem it might represent a light bulb or anything else with resistance.\n5. [![Step 5 Memorize Ohm's Law.](https:\/\/www.wikihow.com\/images\/thumb\/a\/a8\/Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg)\n   5\n   **Memorize Ohm's Law.** There's a very simple relationship between current, voltage, and resistance.[\\[5\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-5) X Research source     Write this down or [memorize](https:\/\/www.wikihow.com\/Improve-Your-Memory \"Improve Your Memory\") it; you'll use it often when solving circuit problems:[\\[6\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-6)X [Expert Source](https:\/\/www.wikihow.com\/wikiHow:Delivering-a-Trustworthy-Experience) [![Mantas Silvanavicius]()Mantas Silvanavicius Licensed Electrician](https:\/\/www.wikihow.com\/Author\/Mantas-Silvanavicius) Expert Interview\n   \n   - Current = voltage divided by resistance\n   - This is usually written: I = V \/ R\n   - Think about what happens when you increase V (voltage) or R (resistance). Does this match what you learned in the explanations above?\n\nPart 2\n\nPart 2 of 3:\n\n### Calculating Voltage across a Resistor (Series Circuit)\n\n[![PDF download](https:\/\/www.wikihow.com\/extensions\/wikihow\/socialstamp\/images\/icon-pdf.svg) Download Article](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\n1. [![Step 1 Understand a series circuit.](https:\/\/www.wikihow.com\/images\/thumb\/e\/e4\/Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg)\n   1\n   **Understand a series circuit.** A [series circuit](https:\/\/www.wikihow.com\/Solve-a-Series-Circuit \"Solve a Series Circuit\") is easy to identify. It's just one loop of wire, with everything arranged in a row. The current flows around the entire loop, going through each resistor or element in order.\n   \n   - The **current** is always the same at any point along the circuit.[\\[7\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-7) X Research source\n   - When calculating voltage, it doesn't matter where the resistor is on the circuit. You can pick up the resistors and move them around, and you'll still have the same voltage across each one.\n   - We'll use an example circuit with three resistors in series: R1, R2, and R3. This is powered by a 12 volt battery. We'll find the voltage across each one.\n2. [![Step 2 Calculate the total resistance.](https:\/\/www.wikihow.com\/images\/thumb\/b\/b8\/Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg)\n   2\n   **Calculate the total resistance.** Add together all resistance values on the circuit. The answer is the total resistance of the series circuit.\n   \n   - For example, the three resistors R1, R2, and R3 have resistances of\n     2 Ω (ohms), 3 Ω, and 5 Ω\n     respectively. The total resistance is 2 + 3 + 5 = 10 ohms.\n3. [![Step 3 Find the current.](https:\/\/www.wikihow.com\/images\/thumb\/5\/58\/Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg)\n   3\n   **Find the current.** Use Ohm's Law to find the current of the entire circuit. Remember, the current is the same anywhere on a series circuit. Once we calculate the current this way, we can use it for all our calculations.[\\[8\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-8) X Research source\n   \n   - Ohm's Law says that the current I = V \/ R. The voltage across the whole circuit is 12 volts, and the total resistance is 10 ohms. The answer is I = 12 \/ 10 =\n     1\\.2 amperes\n     .\n4. [![Step 4 Adjust Ohm's Law to solve for voltage.](https:\/\/www.wikihow.com\/images\/thumb\/8\/88\/Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg)\n   4\n   **Adjust Ohm's Law to solve for voltage.** With basic [algebra](https:\/\/www.wikihow.com\/Learn-Algebra \"Learn Algebra\"), we can change Ohm's Law to solve for voltage instead of current:[\\[9\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-9) X Research source\n   \n   - I = V \/ R\n   - IR = VR \/ R\n   - IR = V\n   - V = IR\n5. [![Step 5 Calculate the voltage across each resistor.](https:\/\/www.wikihow.com\/images\/thumb\/d\/d1\/Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg)\n   5\n   **Calculate the voltage across each resistor.** We know the resistance, we know the current, and we have our equation.[\\[10\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-10) X Research source     Plug in the numbers and solve. Here's our example problem solved for all three resistors:\n   \n   - Voltage across R1 = V1 = (\n     1\\.2A\n     )(\n     2Ω\n     ) = 2.4 volts.\n   - Voltage across R2 = V2 = (\n     1\\.2A\n     )(\n     3Ω\n     ) = 3.6 volts.\n   - Voltage across R3 = V3 = (\n     1\\.2A\n     )(\n     5Ω\n     ) = 6.0 volts.\n6. [![Step 6 Check your answer.](https:\/\/www.wikihow.com\/images\/thumb\/4\/42\/Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg)\n   6\n   **Check your answer.** In a series circuit, the sum of all your answers must equal the total voltage. Add up every voltage you calculated and see if you get the voltage of the entire circuit.[\\[11\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-11) X Research source     If you didn't, go back and check for mistakes.\n   \n   - In our example, 2.4 + 3.6 + 6.0 = 12 volts, the voltage across the whole circuit.\n   - If your answer is slightly off (for instance, 11.97 instead of 12), you probably rounded a number at some point. Your answer is still correct.\n   - Remember, voltage measures the differences in charge, or numbers of electrons. Imagine counting the number of new electrons you see as you travel along the circuit. If you count them correctly, you're going to end up with the total change in electrons from the beginning to the end.\n\nPart 3\n\nPart 3 of 3:\n\n### Calculating Voltage across a Resistor (Parallel Circuit)\n\n[![PDF download](https:\/\/www.wikihow.com\/extensions\/wikihow\/socialstamp\/images\/icon-pdf.svg) Download Article](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\n1. [![Step 1 Understand parallel circuits.](https:\/\/www.wikihow.com\/images\/thumb\/b\/bb\/Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg)\n   1\n   **Understand parallel circuits.** Imagine a wire leaving one end of a battery, then splitting into two separate wires. These two wires run [parallel](https:\/\/www.wikihow.com\/Solve-Parallel-Circuits \"Solve Parallel Circuits\") to each other, then join up again before they reach the other end of the battery. If there's a resistor on the left wire and a resistor on the right wire, those two resistors are connected \"in parallel.\"[\\[12\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-12) X Research source\n   \n   - You can have any number of wires in a parallel circuit. These instructions will still work for a circuit that splits into one hundred wires and comes back together.\n2. [![Step 2 Think about how the current flows.](https:\/\/www.wikihow.com\/images\/thumb\/c\/ce\/Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg)\n   2\n   **Think about how the current flows.** In a parallel circuit, the current flows across each path available to it. Current will flow through the wire on the left, cross the left resistor, and reach the other end. At the same time, current will flow through the wire on the right, cross the right resistor, and reach the end. No part of the current doubles back or flows through two parallel resistors.\n3. [![Step 3 Use the total voltage to find the voltage across each resistor.](https:\/\/www.wikihow.com\/images\/thumb\/d\/d7\/Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg)\n   3\n   **Use the total voltage to find the voltage across each resistor.** If you know the voltage across the whole circuit, the answer is surprisingly easy. Each parallel wire has the same voltage as the entire circuit.[\\[13\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-13) X Research source     Let's say a circuit with two parallel resistors is powered by a 6 volt battery. The voltage across the left resistor is 6 volts, and the voltage across the right resistor is 6 volts. It doesn't even matter how much resistance there is. To understand why, think back to the series circuits described above:\n   \n   - Remember that adding voltage drops in a series circuit always results in the total voltage across the circuit.\n   - Think of each path the current takes as a series circuit. The same holds true for this: if you count up all the voltage drops, you'll end up with the total voltage.\n   - Since the current through each of the two wires only passes through one resistor, the voltage across that resistor must equal the total voltage.\n4. [![Step 4 Calculate the total current of the circuit.](https:\/\/www.wikihow.com\/images\/thumb\/3\/3d\/Calculate-Voltage-Across-a-Resistor-Step-15.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-15.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-15.jpg)\n   4\n   **Calculate the total current of the circuit.** If the problem doesn't tell you what the total voltage of the circuit is, you'll need to complete a few more steps. Start by finding the total current passing through the circuit.[\\[14\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-14) X Research source     In a [parallel circuit](https:\/\/www.wikihow.com\/Make-a-Parallel-Circuit \"Make a Parallel Circuit\"), the total current is equal to the sum of the current running through each parallel path.[\\[15\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-15) X Research source Serway, R.A. and John W. Jewett, Jr., Physics for Scientists and Engineers with Modern Physics. 8th edition. California: Brooks\/Cole. 2010. Ebook\n   \n   - In mathematical terms: Itotal = I1 + I2 + I3...\n   - If you're having trouble understanding this, imagine a water pipe split into two paths. The total amount of water flow is just the amount of water flow in each pipe, added together.\n5. [![Step 5 Compute the total resistance of the circuit.](https:\/\/www.wikihow.com\/images\/thumb\/6\/67\/Calculate-Voltage-Across-a-Resistor-Step-16.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-16.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-16.jpg)\n   5\n   **Compute the total resistance of the circuit.** Resistors are not as effective in a parallel circuit, because they only block the current going along one wire. In fact, the more wires there are, the easier it is for the current to find a way through. To find the total resistance, solve for Rtotal in this equation:[\\[16\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-16) X Research source\n   \n   - 1 \/ Rtotal = 1 \/ R1 + 1 \/ R2 + 1 \/ R3 ...\n   - For example, a circuit has a 2 ohm and a 4 ohm resistor in parallel. 1 \/ Rtotal = 1\/2 + 1\/4 = 3\/4 → 1 = (3\/4)Rtotal → Rtotal = 1\/(3\/4) = 4\/3 = ~1.33 ohms.\n6. [![Step 6 Find the voltage from your answers.](https:\/\/www.wikihow.com\/images\/thumb\/b\/b7\/Calculate-Voltage-Across-a-Resistor-Step-17.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-17.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-17.jpg)\n   6\n   **Find the voltage from your answers.** Remember, once we find the total voltage of the circuit, we have found the voltage across any one of the parallel wires. Solve for the whole circuit using Ohm's law.[\\[17\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-17) X Research source     Here's an example:\n   \n   - A circuit has 5 amperes of current running through it. The total resistance is 1.33 ohms.\n   - According to Ohm's Law, I = V \/ R, therefore V = IR\n   - V = (5A)(1.33Ω) = 6.65 volts.\n\n## Community Q\\&A\nSearch\n\n[Add New Question]()\n\n- Question\n  \n  What is the percentage of applied voltage that will be dropped across r3=70 if r1=80 and r2=50?\n  \n  ![Community Answer](https:\/\/www.wikihow.com\/images\/thumb\/0\/0a\/CommunityAvatar1.png\/-crop-104-104-104px-CommunityAvatar1.png)\n  \n  Community Answer\n  \n  It would be 35%. The higher the resistance, the higher the voltage drop. The ratio of resistances here is 80:50:70. Solving for 70 ohms, we get 35%.\n  \n  **Thanks! We're glad this was helpful.**  \n   **Thank you for your feedback.**  \n    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even \\$1 helps us in our mission.  [Support wikiHow](https:\/\/www.wikihow.com\/wikiHow:Contribute)\n  \n  [Yes](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor) [No](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n  \n  [Not Helpful 17](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor) [Helpful 41](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n- Question\n  \n  What is the voltage of a 60 ohm resistor if the circuit voltage is 150 volts with two parallel 30 ohm resistors and one 60 ohm resister in the series?\n  \n  ![Community Answer](https:\/\/www.wikihow.com\/images\/thumb\/f\/f2\/CommunityAvatar3.png\/-crop-104-104-104px-CommunityAvatar3.png)\n  \n  Community Answer\n  \n  Assuming you intend to ask what is the voltage drop across the 60 ohm resistor, the answer is 120v. The two parallel 30 ohm resistors have an equivalent resistance of 15 ohms. 1\/(1\/30 + 1\/30) = 15. The total resistance appears as 75 ohms to the 150v source. Find the circuit current by I = E\/R or I = 150\/75 = 2 amps. Find the voltage drop for the 60 ohm resistor with E = I x R or E = 2 x 60 = 120V drop across the 60 Ohm resistor.\n  \n  **Thanks! We're glad this was helpful.**  \n   **Thank you for your feedback.**  \n    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even \\$1 helps us in our mission.  [Support wikiHow](https:\/\/www.wikihow.com\/wikiHow:Contribute)\n  \n  [Yes](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor) [No](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n  \n  [Not Helpful 34](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor) [Helpful 44](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n- Question\n  \n  What becomes the Voltage if we use 2 resistors of 4W in parallel?\n  \n  ![Community Answer](https:\/\/www.wikihow.com\/images\/thumb\/0\/0a\/CommunityAvatar1.png\/-crop-104-104-104px-CommunityAvatar1.png)\n  \n  Community Answer\n  \n  As any other data is not provided, the voltage across two resistors of 4w in parallel is the same.\n  \n  **Thanks! We're glad this was helpful.**  \n   **Thank you for your feedback.**  \n    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even \\$1 helps us in our mission.  [Support wikiHow](https:\/\/www.wikihow.com\/wikiHow:Contribute)\n  \n  [Yes](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor) [No](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n  \n  [Not Helpful 16](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor) [Helpful 56](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\n[See more answers](https:\/\/www.wikihow.com\/Questions\/Calculate-Voltage-Across-a-Resistor#offset=3)\n\nAsk a Question\n\n200 characters left\n\nInclude your email address to get a message when this question is answered.\n\n[Submit]()\n\nAdvertisement\n## Video\n## Tips\n- The voltage across a resistor is often called a \"voltage drop.\"\n  Thanks\n  \n  [Helpful 5](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)   [Not Helpful 0](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n- If you have a complicated circuit that involves resistors in series *and* resistors in parallel, pick two nearby resistors. Find the total resistance across them using the rules for resistors in parallel or in series, as appropriate. Now you can treat them as a single resistor. Keep doing this until you have a simple circuit with resistors *either* in parallel *or* in series.\n  Thanks\n  \n  [Helpful 0](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)   [Not Helpful 0](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n- Understand the terminology:\n  \n  - Circuit – composed of elements (e.g. resistors, capacitors, and inductors) connected by wires and wherein current can pass through\n  - Resistors – elements that can reduce or resist current\n  - Current – flow of charge into wires; unit: Ampere, A\n  - Voltage – work done per unit charge; unit: Voltage, V\n  - Resistance – measurement of the opposition of an element to electric current; unit: Ohm, Ω\n  Thanks\n  \n  [Helpful 0](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)   [Not Helpful 0](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\nSubmit a Tip\n\nAll tip submissions are carefully reviewed before being published\n\nName\n\nPlease provide your name and last initial\n\n[Submit](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\nThanks for submitting a tip for review\\!\n\nAdvertisement\n\n## You Might Also Like\n[![Calculate Total Current](https:\/\/www.wikihow.com\/images\/thumb\/a\/aa\/Calculate-Total-Current-Step-18-Version-2.jpg\/-crop-342-184-245px-Calculate-Total-Current-Step-18-Version-2.jpg.webp) How to Calculate Total Current ![](https:\/\/www.wikihow.com\/images\/thumb\/a\/aa\/Calculate-Total-Current-Step-18-Version-2.jpg\/-crop-342-184-245px-Calculate-Total-Current-Step-18-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Total-Current)\n\n[![Solve Parallel Circuits](https:\/\/www.wikihow.com\/images\/thumb\/2\/2a\/492123-16-2.jpg\/-crop-342-184-245px-492123-16-2.jpg.webp) How to Solve Parallel Circuits ![](https:\/\/www.wikihow.com\/images\/thumb\/2\/2a\/492123-16-2.jpg\/-crop-342-184-245px-492123-16-2.jpg)](https:\/\/www.wikihow.com\/Solve-Parallel-Circuits)\n\n[![Calculate Total 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![](https:\/\/www.wikihow.com\/images\/thumb\/6\/62\/Convert-Watts-to-Amps-Step-10.jpg\/-crop-342-184-245px-Convert-Watts-to-Amps-Step-10.jpg)](https:\/\/www.wikihow.com\/Convert-Watts-to-Amps)\n\n[![Wire a Variable or Fixed Speed DC Motor Circuit](https:\/\/www.wikihow.com\/images\/thumb\/d\/dc\/WVFSDMC_2_6.jpg\/-crop-342-184-217px-WVFSDMC_2_6.jpg.webp) How to Wire a Variable or Fixed Speed DC Motor Circuit ![](https:\/\/www.wikihow.com\/images\/thumb\/d\/dc\/WVFSDMC_2_6.jpg\/-crop-342-184-217px-WVFSDMC_2_6.jpg)](https:\/\/www.wikihow.com\/Wire-a-Variable-or-Fixed-Speed-DC-Motor-Circuit)\n\nAdvertisement\n\n## References\n1. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-1) Serway, R.A. and John W. Jewett, Jr., Physics for Scientists and Engineers with Modern Physics. 8th edition. California: Brooks\/Cole. 2010. Ebook\n2. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-2) <https:\/\/energyeducation.ca\/encyclopedia\/Electric_charge>\n3. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-3) <https:\/\/www.education.vic.gov.au\/school\/teachers\/teachingresources\/discipline\/science\/continuum\/Pages\/voltage.aspx>\n4. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-4) <https:\/\/www.physicsclassroom.com\/class\/circuits\/Lesson-3\/Resistance>\n5. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-5) <https:\/\/phet.colorado.edu\/en\/simulations\/ohms-law>\n6. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-6) Mantas Silvanavicius. Licensed Electrician. Expert Interview\n7. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-7) <https:\/\/energyeducation.ca\/encyclopedia\/Series_circuit>\n8. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-8) <https:\/\/www.calculator.net\/ohms-law-calculator.html>\n9. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-9) <https:\/\/www.hsa.org.uk\/electricity\/current-voltage-and-resistance>\n\n[More References (8)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#aiinfo)\n\n1. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-10) <https:\/\/pressbooks.bccampus.ca\/collegephysics\/chapter\/resistors-in-series-and-parallel\/>\n2. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-11) <https:\/\/pressbooks.bccampus.ca\/collegephysics\/chapter\/resistors-in-series-and-parallel\/>\n3. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-12) <https:\/\/www.allaboutcircuits.com\/textbook\/direct-current\/chpt-5\/simple-parallel-circuits\/>\n4. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-13) <https:\/\/www.physicsclassroom.com\/class\/circuits\/Lesson-4\/Parallel-Circuits>\n5. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-14) <https:\/\/pressbooks.bccampus.ca\/basicelectricity\/chapter\/ground\/>\n6. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-15) Serway, R.A. and John W. Jewett, Jr., Physics for Scientists and Engineers with Modern Physics. 8th edition. California: Brooks\/Cole. 2010. Ebook\n7. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-16) [https:\/\/phys.libretexts.org\/Bookshelves\/University\\_Physics\/University\\_Physics\\_(OpenStax)\/University\\_Physics\\_II\\_-\\_Thermodynamics\\_Electricity\\_and\\_Magnetism\\_(OpenStax)\/10%3A\\_Direct-Current\\_Circuits\/10.03%3A\\_Resistors\\_in\\_Series\\_and\\_Parallel](https:\/\/phys.libretexts.org\/Bookshelves\/University_Physics\/University_Physics_\$OpenStax\$\/University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_\$OpenStax\$\/10%3A_Direct-Current_Circuits\/10.03%3A_Resistors_in_Series_and_Parallel)\n8. [↑](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_ref-17) [https:\/\/phys.libretexts.org\/Bookshelves\/University\\_Physics\/University\\_Physics\\_(OpenStax)\/University\\_Physics\\_II\\_-\\_Thermodynamics\\_Electricity\\_and\\_Magnetism\\_(OpenStax)\/10%3A\\_Direct-Current\\_Circuits\/10.03%3A\\_Resistors\\_in\\_Series\\_and\\_Parallel](https:\/\/phys.libretexts.org\/Bookshelves\/University_Physics\/University_Physics_\$OpenStax\$\/University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_\$OpenStax\$\/10%3A_Direct-Current_Circuits\/10.03%3A_Resistors_in_Series_and_Parallel)\n\n## About This Article\nMS\n\nCo-authored by:\n\n[Mantas Silvanavicius](https:\/\/www.wikihow.com\/Author\/Mantas-Silvanavicius)\n\nLicensed Electrician\n\nThis article was co-authored by [Mantas Silvanavicius](https:\/\/www.wikihow.com\/Author\/Mantas-Silvanavicius). Mantas Silvanavicius is a Licensed Electrician and the Owner of M+S Electric based in Las Vegas, Nevada. With more than 20 years of experience, he specializes in home electrical installations, testing, and wiring. Mantas and his team have completed projects for companies such as Seiko and Springhill Suites by Marriott. M+S Electric is licensed, bonded, and insured. This article has been viewed 1,032,909 times.\n\n27 votes - 81%\n\nCo-authors: 13\n\nUpdated: September 7, 2024\n\nViews: 1,032,909\n\nCategories: [Electromagnetism](https:\/\/www.wikihow.com\/Category:Electromagnetism \"Category:Electromagnetism\")\n\n[Article SummaryX](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#summary_wrapper)\n\nTo calculate voltage across a resistor in a series circuit, start by adding together all of the resistance values in the circuit. Then, divide the voltage across the circuit by the total resistance to find the current. Once you have the current, calculate voltage for the individual resistors by multiplying the current by the resistance. For example, in a series circuit with 3 resistors of 2, 3 and 5 Ohms, and a voltage of 12 volts, the current would be 12 divided by 10, or 1.2 amperes. For the 2 Ohm resistor, the voltage would be 1.2 times 2, or 2.4 volts. 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By continuing to use our site, you agree to our [cookie policy](https:\/\/www.wikihow.com\/wikiHow:Cookie-Policy).\n\nMS\n\nCo-authored by:\n\n[Mantas Silvanavicius](https:\/\/www.wikihow.com\/Author\/Mantas-Silvanavicius)\n\nLicensed Electrician\n\nCo-authors: 13\n\nUpdated: September 7, 2024\n\nViews: 1,032,909\n\n81% of readers found this article **helpful**.\n\n27 votes - 81%\n\nClick a star to add your vote\n\n![Mohd Rodzi Mohamad](https:\/\/www.wikihow.com\/images\/thumb\/f\/f5\/CommunityAvatar4.png\/-crop-72-72-72px-CommunityAvatar4.png)\n\nMohd Rodzi Mohamad\n\nAug 26, 2016\n\n\"This article is very neatly and clearly explained with illustrations of pictures for better comprehension. Very helpful for electronic and electrical students, technicians and even hobbyists. Simple vocabulary makes it easy to follow, too. Thank you.\"...\" [more](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\n![Sachintha Kolugala](https:\/\/www.wikihow.com\/images\/thumb\/f\/f2\/CommunityAvatar3.png\/-crop-72-72-72px-CommunityAvatar3.png)\n\nSachintha Kolugala\n\nMay 17, 2016\n\n\"I was lost in currents and voltages. But this article really helped me to take it in easier way. Educational articles can only give us the details, but this is so encouraging. Thank you, wikiHow!\"...\" [more](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\n![Ale C.](https:\/\/www.wikihow.com\/images\/thumb\/0\/0a\/CommunityAvatar1.png\/-crop-72-72-72px-CommunityAvatar1.png)\n\nAle C.\n\nOct 4, 2016\n\n\"This wikiHow article summarized multiple wordy textbook pages into a few slides with visual and text explanations. 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Questions? Please contact support@wikihow.pro.\n\n## Thank You\nWe've emailed you a copy of your image, and you can also download it below.\n\n[Download HD Image](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\nBy continuing to use wikiHow, you agree to our  \n[Terms of Service](https:\/\/www.wikihow.com\/wikiHow:Terms-of-Use) and [Privacy Policy](https:\/\/www.wikihow.com\/wikiHow:Privacy-Policy).  \n  \nwikiHow Pro is intended only for your personal, non-commercial use. wikiHow, Inc. reserves the right to terminate subscriptions to wikiHow Pro at any time and for any reason.  \n  \nQuestions? Please contact [support@wikihow.pro](mailto:support@wikihow.pro).\n\nSomething went wrong\n\n[Dismiss]()","attrs_readable_markdown":"[![PDF download](https:\/\/www.wikihow.com\/extensions\/wikihow\/socialstamp\/images\/icon-pdf.svg) Download Article](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\n[![PDF download](https:\/\/www.wikihow.com\/extensions\/wikihow\/socialstamp\/images\/icon-pdf.svg) Download Article](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n\nBefore you can calculate the voltage across a resistor, you'll first have to determine what kind of circuit you are using. If you need a review of the basic terms or a little help understanding [circuits](https:\/\/www.wikihow.com\/Make-a-Simple-Electrical-Circuit \"Make a Simple Electrical Circuit\"), start with the first section. Otherwise, jump ahead to the type of circuit you have to solve.\n\n1. [![Step 1 Learn about current.](https:\/\/www.wikihow.com\/images\/thumb\/2\/2b\/Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg)\n   Let’s think about current by using an analogy: imagine you pour a bag of corn kernels into a bowl. Each corn kernel is an [electron](https:\/\/www.wikihow.com\/Find-Electrons \"Find Electrons\"), and the stream of kernels flowing into the bowl is the current.[\\[1\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-1)  When talking about the flow, you describe it by saying how many kernels are flowing each second. When talking about a current, you measure it in **amperes** ([amps](https:\/\/www.wikihow.com\/Find-Amps \"Find Amps\")), or a certain (very large) number of electrons flowing per second.\n2. [![Step 2 Think about electrical charge.](https:\/\/www.wikihow.com\/images\/thumb\/a\/a1\/Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg)\n   Electrons have a \"negative\" electrical charge. This means they attract (or flow toward) objects with a positive charge, and repel (or flow away from) objects with a negative charge. Since they're all negative, electrons are always trying to push away from other electrons, spreading out wherever they can.[\\[2\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-2)\n   Advertisement\n3. [![Step 3 Understand voltage.](https:\/\/www.wikihow.com\/images\/thumb\/7\/79\/Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg)\n   [Voltage](https:\/\/www.wikihow.com\/Test-Voltage-with-a-Multimeter \"Test Voltage with a Multimeter\") measures the difference in electrical charge between two points.[\\[3\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-3)  The greater the difference, the more energetically the two sides attract each other. Here's an example with an everyday battery:\n   \n   - Inside a battery, chemical reactions happen that produces a buildup of electrons. The electrons go to the negative end, while the positive end stays mostly empty. (These are called the negative and positive terminals.) The longer this goes on, the larger the voltage between the two ends.\n   - When you connect a wire between the negative and positive ends, the electrons at the negative end suddenly have somewhere to go. They shoot toward the positive end, creating a current. The larger the voltage, the more electrons move to the positive end each second.\n4. [![Step 4 Figure out resistance.](https:\/\/www.wikihow.com\/images\/thumb\/5\/55\/Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg)\n   [Resistance](https:\/\/www.wikihow.com\/Measure-Resistance \"Measure Resistance\") is exactly what it sounds like. The more resistance something has, the harder it is for the electrons to push through. This slows the current, since fewer electrons can push through each second.[\\[4\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-4)\n   \n   - A resistor is anything in the circuit that adds resistance. You can buy an actual \"resistor\" at an electronics store, but in a circuits problem it might represent a light bulb or anything else with resistance.\n5. [![Step 5 Memorize Ohm's Law.](https:\/\/www.wikihow.com\/images\/thumb\/a\/a8\/Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg)\n   There's a very simple relationship between current, voltage, and resistance.[\\[5\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-5)  Write this down or [memorize](https:\/\/www.wikihow.com\/Improve-Your-Memory \"Improve Your Memory\") it; you'll use it often when solving circuit problems:[\\[6\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-6)\n   \n   - Current = voltage divided by resistance\n   - This is usually written: I = V \/ R\n   - Think about what happens when you increase V (voltage) or R (resistance). Does this match what you learned in the explanations above?\n\n1. [![Step 1 Understand a series circuit.](https:\/\/www.wikihow.com\/images\/thumb\/e\/e4\/Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg)\n   A [series circuit](https:\/\/www.wikihow.com\/Solve-a-Series-Circuit \"Solve a Series Circuit\") is easy to identify. It's just one loop of wire, with everything arranged in a row. The current flows around the entire loop, going through each resistor or element in order.\n   \n   - The **current** is always the same at any point along the circuit.[\\[7\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-7)\n   - When calculating voltage, it doesn't matter where the resistor is on the circuit. You can pick up the resistors and move them around, and you'll still have the same voltage across each one.\n   - We'll use an example circuit with three resistors in series: R1, R2, and R3. This is powered by a 12 volt battery. We'll find the voltage across each one.\n2. [![Step 2 Calculate the total resistance.](https:\/\/www.wikihow.com\/images\/thumb\/b\/b8\/Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg)\n   Add together all resistance values on the circuit. The answer is the total resistance of the series circuit.\n   \n   - For example, the three resistors R1, R2, and R3 have resistances of 2 Ω (ohms), 3 Ω, and 5 Ω respectively. The total resistance is 2 + 3 + 5 = 10 ohms.\n3. [![Step 3 Find the current.](https:\/\/www.wikihow.com\/images\/thumb\/5\/58\/Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg)\n   Use Ohm's Law to find the current of the entire circuit. Remember, the current is the same anywhere on a series circuit. Once we calculate the current this way, we can use it for all our calculations.[\\[8\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-8)\n   \n   - Ohm's Law says that the current I = V \/ R. The voltage across the whole circuit is 12 volts, and the total resistance is 10 ohms. The answer is I = 12 \/ 10 = 1\\.2 amperes.\n4. [![Step 4 Adjust Ohm's Law to solve for voltage.](https:\/\/www.wikihow.com\/images\/thumb\/8\/88\/Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg)\n   With basic [algebra](https:\/\/www.wikihow.com\/Learn-Algebra \"Learn Algebra\"), we can change Ohm's Law to solve for voltage instead of current:[\\[9\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-9)\n   \n   - I = V \/ R\n   - IR = VR \/ R\n   - IR = V\n   - V = IR\n5. [![Step 5 Calculate the voltage across each resistor.](https:\/\/www.wikihow.com\/images\/thumb\/d\/d1\/Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg)\n   We know the resistance, we know the current, and we have our equation.[\\[10\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-10)  Plug in the numbers and solve. Here's our example problem solved for all three resistors:\n   \n   - Voltage across R1 = V1 = (1\\.2A)(2Ω) = 2.4 volts.\n   - Voltage across R2 = V2 = (1\\.2A)(3Ω) = 3.6 volts.\n   - Voltage across R3 = V3 = (1\\.2A)(5Ω) = 6.0 volts.\n6. [![Step 6 Check your answer.](https:\/\/www.wikihow.com\/images\/thumb\/4\/42\/Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg)\n   In a series circuit, the sum of all your answers must equal the total voltage. Add up every voltage you calculated and see if you get the voltage of the entire circuit.[\\[11\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-11)  If you didn't, go back and check for mistakes.\n   \n   - In our example, 2.4 + 3.6 + 6.0 = 12 volts, the voltage across the whole circuit.\n   - If your answer is slightly off (for instance, 11.97 instead of 12), you probably rounded a number at some point. Your answer is still correct.\n   - Remember, voltage measures the differences in charge, or numbers of electrons. Imagine counting the number of new electrons you see as you travel along the circuit. If you count them correctly, you're going to end up with the total change in electrons from the beginning to the end.\n\n1. [![Step 1 Understand parallel circuits.](https:\/\/www.wikihow.com\/images\/thumb\/b\/bb\/Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg)\n   Imagine a wire leaving one end of a battery, then splitting into two separate wires. These two wires run [parallel](https:\/\/www.wikihow.com\/Solve-Parallel-Circuits \"Solve Parallel Circuits\") to each other, then join up again before they reach the other end of the battery. If there's a resistor on the left wire and a resistor on the right wire, those two resistors are connected \"in parallel.\"[\\[12\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-12)\n   \n   - You can have any number of wires in a parallel circuit. These instructions will still work for a circuit that splits into one hundred wires and comes back together.\n2. [![Step 2 Think about how the current flows.](https:\/\/www.wikihow.com\/images\/thumb\/c\/ce\/Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg)\n   In a parallel circuit, the current flows across each path available to it. Current will flow through the wire on the left, cross the left resistor, and reach the other end. At the same time, current will flow through the wire on the right, cross the right resistor, and reach the end. No part of the current doubles back or flows through two parallel resistors.\n3. [![Step 3 Use the total voltage to find the voltage across each resistor.](https:\/\/www.wikihow.com\/images\/thumb\/d\/d7\/Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg)\n   If you know the voltage across the whole circuit, the answer is surprisingly easy. Each parallel wire has the same voltage as the entire circuit.[\\[13\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-13)  Let's say a circuit with two parallel resistors is powered by a 6 volt battery. The voltage across the left resistor is 6 volts, and the voltage across the right resistor is 6 volts. It doesn't even matter how much resistance there is. To understand why, think back to the series circuits described above:\n   \n   - Remember that adding voltage drops in a series circuit always results in the total voltage across the circuit.\n   - Think of each path the current takes as a series circuit. The same holds true for this: if you count up all the voltage drops, you'll end up with the total voltage.\n   - Since the current through each of the two wires only passes through one resistor, the voltage across that resistor must equal the total voltage.\n4. [![Step 4 Calculate the total current of the circuit.](https:\/\/www.wikihow.com\/images\/thumb\/3\/3d\/Calculate-Voltage-Across-a-Resistor-Step-15.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-15.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-15.jpg)\n   If the problem doesn't tell you what the total voltage of the circuit is, you'll need to complete a few more steps. Start by finding the total current passing through the circuit.[\\[14\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-14)  In a [parallel circuit](https:\/\/www.wikihow.com\/Make-a-Parallel-Circuit \"Make a Parallel Circuit\"), the total current is equal to the sum of the current running through each parallel path.[\\[15\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-15)\n   \n   - In mathematical terms: Itotal = I1 + I2 + I3...\n   - If you're having trouble understanding this, imagine a water pipe split into two paths. The total amount of water flow is just the amount of water flow in each pipe, added together.\n5. [![Step 5 Compute the total resistance of the circuit.](https:\/\/www.wikihow.com\/images\/thumb\/6\/67\/Calculate-Voltage-Across-a-Resistor-Step-16.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-16.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-16.jpg)\n   Resistors are not as effective in a parallel circuit, because they only block the current going along one wire. In fact, the more wires there are, the easier it is for the current to find a way through. To find the total resistance, solve for Rtotal in this equation:[\\[16\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-16)\n   \n   - 1 \/ Rtotal = 1 \/ R1 + 1 \/ R2 + 1 \/ R3 ...\n   - For example, a circuit has a 2 ohm and a 4 ohm resistor in parallel. 1 \/ Rtotal = 1\/2 + 1\/4 = 3\/4 → 1 = (3\/4)Rtotal → Rtotal = 1\/(3\/4) = 4\/3 = ~1.33 ohms.\n6. [![Step 6 Find the voltage from your answers.](https:\/\/www.wikihow.com\/images\/thumb\/b\/b7\/Calculate-Voltage-Across-a-Resistor-Step-17.jpg\/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-17.jpg)](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#\/Image:Calculate-Voltage-Across-a-Resistor-Step-17.jpg)\n   Remember, once we find the total voltage of the circuit, we have found the voltage across any one of the parallel wires. Solve for the whole circuit using Ohm's law.[\\[17\\]](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#_note-17)  Here's an example:\n   \n   - A circuit has 5 amperes of current running through it. The total resistance is 1.33 ohms.\n   - According to Ohm's Law, I = V \/ R, therefore V = IR\n   - V = (5A)(1.33Ω) = 6.65 volts.\n\nSearch\n\n[Add New Question]()\n\n- Question\n  \n  What is the percentage of applied voltage that will be dropped across r3=70 if r1=80 and r2=50?\n  \n  ![Community Answer](https:\/\/www.wikihow.com\/images\/thumb\/0\/0a\/CommunityAvatar1.png\/-crop-104-104-104px-CommunityAvatar1.png)\n  \n  Community Answer\n  \n  It would be 35%. The higher the resistance, the higher the voltage drop. The ratio of resistances here is 80:50:70. Solving for 70 ohms, we get 35%.\n- Question\n  \n  What is the voltage of a 60 ohm resistor if the circuit voltage is 150 volts with two parallel 30 ohm resistors and one 60 ohm resister in the series?\n  \n  ![Community Answer](https:\/\/www.wikihow.com\/images\/thumb\/f\/f2\/CommunityAvatar3.png\/-crop-104-104-104px-CommunityAvatar3.png)\n  \n  Community Answer\n  \n  Assuming you intend to ask what is the voltage drop across the 60 ohm resistor, the answer is 120v. The two parallel 30 ohm resistors have an equivalent resistance of 15 ohms. 1\/(1\/30 + 1\/30) = 15. The total resistance appears as 75 ohms to the 150v source. Find the circuit current by I = E\/R or I = 150\/75 = 2 amps. Find the voltage drop for the 60 ohm resistor with E = I x R or E = 2 x 60 = 120V drop across the 60 Ohm resistor.\n- Question\n  \n  What becomes the Voltage if we use 2 resistors of 4W in parallel?\n  \n  ![Community Answer](https:\/\/www.wikihow.com\/images\/thumb\/0\/0a\/CommunityAvatar1.png\/-crop-104-104-104px-CommunityAvatar1.png)\n  \n  Community Answer\n  \n  As any other data is not provided, the voltage across two resistors of 4w in parallel is the same.\n\n[See more answers](https:\/\/www.wikihow.com\/Questions\/Calculate-Voltage-Across-a-Resistor#offset=3)\n\nAsk a Question\n\n200 characters left\n\nInclude your email address to get a message when this question is answered.\n\n[Submit]()\n\nAdvertisement\n## Video\n- The voltage across a resistor is often called a \"voltage drop.\"\n  Thanks\n- If you have a complicated circuit that involves resistors in series *and* resistors in parallel, pick two nearby resistors. Find the total resistance across them using the rules for resistors in parallel or in series, as appropriate. Now you can treat them as a single resistor. Keep doing this until you have a simple circuit with resistors *either* in parallel *or* in series.\n  Thanks\n- Understand the terminology:\n  \n  - Circuit – composed of elements (e.g. resistors, capacitors, and inductors) connected by wires and wherein current can pass through\n  - Resistors – elements that can reduce or resist current\n  - Current – flow of charge into wires; unit: Ampere, A\n  - Voltage – work done per unit charge; unit: Voltage, V\n  - Resistance – measurement of the opposition of an element to electric current; unit: Ohm, Ω\n  Thanks\n\nThanks for submitting a tip for review\\!\n\nAdvertisement\n## References\nAbout This Article\n\n[Article SummaryX](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor#summary_wrapper)\n\nTo calculate voltage across a resistor in a series circuit, start by adding together all of the resistance values in the circuit. Then, divide the voltage across the circuit by the total resistance to find the current. Once you have the current, calculate voltage for the individual resistors by multiplying the current by the resistance. For example, in a series circuit with 3 resistors of 2, 3 and 5 Ohms, and a voltage of 12 volts, the current would be 12 divided by 10, or 1.2 amperes. For the 2 Ohm resistor, the voltage would be 1.2 times 2, or 2.4 volts. If you want to learn how to calculate voltage in a parallel circuit, keep reading the article\\!\n\nDid this summary help you?\n\nThanks to all authors for creating a page that has been read 1,032,909 times.\n\nReader Success Stories\n\n- ![Mohd Rodzi Mohamad](https:\/\/www.wikihow.com\/images\/thumb\/0\/0a\/CommunityAvatar1.png\/-crop-72-72-72px-CommunityAvatar1.png)\n  \n  Mohd Rodzi Mohamad\n  \n  Aug 26, 2016\n  \"This article is very neatly and clearly explained with illustrations of pictures for better comprehension. Very...\" [more](https:\/\/www.wikihow.com\/Calculate-Voltage-Across-a-Resistor)\n## Did this article help you?","meta_canonical":null}

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Boilerpipe Text	Download Article Download Article Before you can calculate the voltage across a resistor, you'll first have to determine what kind of circuit you are using. If you need a review of the basic terms or a little help understanding circuits , start with the first section. Otherwise, jump ahead to the type of circuit you have to solve. Let’s think about current by using an analogy: imagine you pour a bag of corn kernels into a bowl. Each corn kernel is an electron , and the stream of kernels flowing into the bowl is the current. [1] When talking about the flow, you describe it by saying how many kernels are flowing each second. When talking about a current, you measure it in amperes ( amps ), or a certain (very large) number of electrons flowing per second. Electrons have a "negative" electrical charge. This means they attract (or flow toward) objects with a positive charge, and repel (or flow away from) objects with a negative charge. Since they're all negative, electrons are always trying to push away from other electrons, spreading out wherever they can. [2] Advertisement Voltage measures the difference in electrical charge between two points. [3] The greater the difference, the more energetically the two sides attract each other. Here's an example with an everyday battery: Inside a battery, chemical reactions happen that produces a buildup of electrons. The electrons go to the negative end, while the positive end stays mostly empty. (These are called the negative and positive terminals.) The longer this goes on, the larger the voltage between the two ends. When you connect a wire between the negative and positive ends, the electrons at the negative end suddenly have somewhere to go. They shoot toward the positive end, creating a current. The larger the voltage, the more electrons move to the positive end each second. Resistance is exactly what it sounds like. The more resistance something has, the harder it is for the electrons to push through. This slows the current, since fewer electrons can push through each second. [4] A resistor is anything in the circuit that adds resistance. You can buy an actual "resistor" at an electronics store, but in a circuits problem it might represent a light bulb or anything else with resistance. There's a very simple relationship between current, voltage, and resistance. [5] Write this down or memorize it; you'll use it often when solving circuit problems: [6] Current = voltage divided by resistance This is usually written: I = V / R Think about what happens when you increase V (voltage) or R (resistance). Does this match what you learned in the explanations above? Advertisement A series circuit is easy to identify. It's just one loop of wire, with everything arranged in a row. The current flows around the entire loop, going through each resistor or element in order. The current is always the same at any point along the circuit. [7] When calculating voltage, it doesn't matter where the resistor is on the circuit. You can pick up the resistors and move them around, and you'll still have the same voltage across each one. We'll use an example circuit with three resistors in series: R 1 , R 2 , and R 3 . This is powered by a 12 volt battery. We'll find the voltage across each one. Add together all resistance values on the circuit. The answer is the total resistance of the series circuit. For example, the three resistors R 1 , R 2 , and R 3 have resistances of 2 Ω (ohms), 3 Ω, and 5 Ω respectively. The total resistance is 2 + 3 + 5 = 10 ohms. Use Ohm's Law to find the current of the entire circuit. Remember, the current is the same anywhere on a series circuit. Once we calculate the current this way, we can use it for all our calculations. [8] Ohm's Law says that the current I = V / R . The voltage across the whole circuit is 12 volts, and the total resistance is 10 ohms. The answer is I = 12 / 10 = 1.2 amperes . With basic algebra , we can change Ohm's Law to solve for voltage instead of current: [9] I = V / R IR = V R / R IR = V V = IR We know the resistance, we know the current, and we have our equation. [10] Plug in the numbers and solve. Here's our example problem solved for all three resistors: Voltage across R 1 = V 1 = ( 1.2A )( 2Ω ) = 2.4 volts. Voltage across R 2 = V 2 = ( 1.2A )( 3Ω ) = 3.6 volts. Voltage across R 3 = V 3 = ( 1.2A )( 5Ω ) = 6.0 volts. In a series circuit, the sum of all your answers must equal the total voltage. Add up every voltage you calculated and see if you get the voltage of the entire circuit. [11] If you didn't, go back and check for mistakes. In our example, 2.4 + 3.6 + 6.0 = 12 volts, the voltage across the whole circuit. If your answer is slightly off (for instance, 11.97 instead of 12), you probably rounded a number at some point. Your answer is still correct. Remember, voltage measures the differences in charge, or numbers of electrons. Imagine counting the number of new electrons you see as you travel along the circuit. If you count them correctly, you're going to end up with the total change in electrons from the beginning to the end. Advertisement Imagine a wire leaving one end of a battery, then splitting into two separate wires. These two wires run parallel to each other, then join up again before they reach the other end of the battery. If there's a resistor on the left wire and a resistor on the right wire, those two resistors are connected "in parallel." [12] You can have any number of wires in a parallel circuit. These instructions will still work for a circuit that splits into one hundred wires and comes back together. In a parallel circuit, the current flows across each path available to it. Current will flow through the wire on the left, cross the left resistor, and reach the other end. At the same time, current will flow through the wire on the right, cross the right resistor, and reach the end. No part of the current doubles back or flows through two parallel resistors. If you know the voltage across the whole circuit, the answer is surprisingly easy. Each parallel wire has the same voltage as the entire circuit. [13] Let's say a circuit with two parallel resistors is powered by a 6 volt battery. The voltage across the left resistor is 6 volts, and the voltage across the right resistor is 6 volts. It doesn't even matter how much resistance there is. To understand why, think back to the series circuits described above: Remember that adding voltage drops in a series circuit always results in the total voltage across the circuit. Think of each path the current takes as a series circuit. The same holds true for this: if you count up all the voltage drops, you'll end up with the total voltage. Since the current through each of the two wires only passes through one resistor, the voltage across that resistor must equal the total voltage. If the problem doesn't tell you what the total voltage of the circuit is, you'll need to complete a few more steps. Start by finding the total current passing through the circuit. [14] In a parallel circuit , the total current is equal to the sum of the current running through each parallel path. [15] In mathematical terms: I total = I 1 + I 2 + I 3 ... If you're having trouble understanding this, imagine a water pipe split into two paths. The total amount of water flow is just the amount of water flow in each pipe, added together. Resistors are not as effective in a parallel circuit, because they only block the current going along one wire. In fact, the more wires there are, the easier it is for the current to find a way through. To find the total resistance, solve for R total in this equation: [16] 1 / R total = 1 / R 1 + 1 / R 2 + 1 / R 3 ... For example, a circuit has a 2 ohm and a 4 ohm resistor in parallel. 1 / R total = 1/2 + 1/4 = 3/4 → 1 = (3/4)R total → R total = 1/(3/4) = 4/3 = ~1.33 ohms. Remember, once we find the total voltage of the circuit, we have found the voltage across any one of the parallel wires. Solve for the whole circuit using Ohm's law. [17] Here's an example: A circuit has 5 amperes of current running through it. The total resistance is 1.33 ohms. According to Ohm's Law, I = V / R, therefore V = IR V = (5A)(1.33Ω) = 6.65 volts. Advertisement Search Add New Question Question What is the percentage of applied voltage that will be dropped across r3=70 if r1=80 and r2=50? Community Answer It would be 35%. The higher the resistance, the higher the voltage drop. The ratio of resistances here is 80:50:70. Solving for 70 ohms, we get 35%. Question What is the voltage of a 60 ohm resistor if the circuit voltage is 150 volts with two parallel 30 ohm resistors and one 60 ohm resister in the series? Community Answer Assuming you intend to ask what is the voltage drop across the 60 ohm resistor, the answer is 120v. The two parallel 30 ohm resistors have an equivalent resistance of 15 ohms. 1/(1/30 + 1/30) = 15. The total resistance appears as 75 ohms to the 150v source. Find the circuit current by I = E/R or I = 150/75 = 2 amps. Find the voltage drop for the 60 ohm resistor with E = I x R or E = 2 x 60 = 120V drop across the 60 Ohm resistor. Question What becomes the Voltage if we use 2 resistors of 4W in parallel? Community Answer As any other data is not provided, the voltage across two resistors of 4w in parallel is the same. See more answers Ask a Question 200 characters left Include your email address to get a message when this question is answered. Submit Advertisement Video The voltage across a resistor is often called a "voltage drop." Thanks If you have a complicated circuit that involves resistors in series and resistors in parallel, pick two nearby resistors. Find the total resistance across them using the rules for resistors in parallel or in series, as appropriate. Now you can treat them as a single resistor. Keep doing this until you have a simple circuit with resistors either in parallel or in series. Thanks Understand the terminology: Circuit – composed of elements (e.g. resistors, capacitors, and inductors) connected by wires and wherein current can pass through Resistors – elements that can reduce or resist current Current – flow of charge into wires; unit: Ampere, A Voltage – work done per unit charge; unit: Voltage, V Resistance – measurement of the opposition of an element to electric current; unit: Ohm, Ω Thanks Thanks for submitting a tip for review! Advertisement References About This Article Article Summary X To calculate voltage across a resistor in a series circuit, start by adding together all of the resistance values in the circuit. Then, divide the voltage across the circuit by the total resistance to find the current. Once you have the current, calculate voltage for the individual resistors by multiplying the current by the resistance. For example, in a series circuit with 3 resistors of 2, 3 and 5 Ohms, and a voltage of 12 volts, the current would be 12 divided by 10, or 1.2 amperes. For the 2 Ohm resistor, the voltage would be 1.2 times 2, or 2.4 volts. If you want to learn how to calculate voltage in a parallel circuit, keep reading the article! Did this summary help you? Thanks to all authors for creating a page that has been read 1,032,909 times. Reader Success Stories Mohd Rodzi Mohamad Aug 26, 2016 "This article is very neatly and clearly explained with illustrations of pictures for better comprehension. 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Learn why people trust wikiHow](https://www.wikihow.com/wikiHow:Delivering-a-Trustworthy-Experience) - [Categories](https://www.wikihow.com/Special:CategoryListing "Special:CategoryListing") - [Education and Communications](https://www.wikihow.com/Category:Education-and-Communications "Category:Education and Communications") - [Studying](https://www.wikihow.com/Category:Studying "Category:Studying") - [Science](https://www.wikihow.com/Category:Science "Category:Science") - [Physics](https://www.wikihow.com/Category:Physics "Category:Physics") - [Electromagnetism](https://www.wikihow.com/Category:Electromagnetism "Category:Electromagnetism") # [How to Calculate Voltage Across a Resistor](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [![PDF download](https://www.wikihow.com/extensions/wikihow/socialstamp/images/icon-pdf.svg) Download Article](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) Explore this Article parts [1 Understanding Circuits](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#Understanding-Circuits) [2 Calculating Voltage across a Resistor (Series Circuit)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#Calculating-Voltage-across-a-Resistor-.28Series-Circuit.29) [3 Calculating Voltage across a Resistor (Parallel Circuit)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#Calculating-Voltage-across-a-Resistor-.28Parallel-Circuit.29) Other Sections [Questions & Answers](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#qa_headline) [Video](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#Video) [Tips and Warnings](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#tips) [Related Articles](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#relatedwikihows) [References](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#References) [Article Summary](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#summary_wrapper) Co-authored by [Mantas Silvanavicius](https://www.wikihow.com/Author/Mantas-Silvanavicius) [Last Updated: September 7, 2024](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Fact Checked](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [![PDF download](https://www.wikihow.com/extensions/wikihow/socialstamp/images/icon-pdf.svg) Download Article](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) X This article was co-authored by [Mantas Silvanavicius](https://www.wikihow.com/Author/Mantas-Silvanavicius). Mantas Silvanavicius is a Licensed Electrician and the Owner of M+S Electric based in Las Vegas, Nevada. With more than 20 years of experience, he specializes in home electrical installations, testing, and wiring. Mantas and his team have completed projects for companies such as Seiko and Springhill Suites by Marriott. M+S Electric is licensed, bonded, and insured. There are [14 references](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#References) cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 1,032,909 times. Before you can calculate the voltage across a resistor, you'll first have to determine what kind of circuit you are using. If you need a review of the basic terms or a little help understanding [circuits](https://www.wikihow.com/Make-a-Simple-Electrical-Circuit "Make a Simple Electrical Circuit"), start with the first section. Otherwise, jump ahead to the type of circuit you have to solve. ## Steps Part 1 Part 1 of 3: ### Understanding Circuits [![PDF download](https://www.wikihow.com/extensions/wikihow/socialstamp/images/icon-pdf.svg) Download Article](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) 1. [![Step 1 Learn about current.](https://www.wikihow.com/images/thumb/2/2b/Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg) 1 Learn about current. Let’s think about current by using an analogy: imagine you pour a bag of corn kernels into a bowl. Each corn kernel is an [electron](https://www.wikihow.com/Find-Electrons "Find Electrons"), and the stream of kernels flowing into the bowl is the current.[\[1\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-1) X Research source Serway, R.A. and John W. Jewett, Jr., Physics for Scientists and Engineers with Modern Physics. 8th edition. California: Brooks/Cole. 2010. Ebook When talking about the flow, you describe it by saying how many kernels are flowing each second. When talking about a current, you measure it in amperes ([amps](https://www.wikihow.com/Find-Amps "Find Amps")), or a certain (very large) number of electrons flowing per second. 2. [![Step 2 Think about electrical charge.](https://www.wikihow.com/images/thumb/a/a1/Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg) 2 Think about electrical charge. Electrons have a "negative" electrical charge. This means they attract (or flow toward) objects with a positive charge, and repel (or flow away from) objects with a negative charge. Since they're all negative, electrons are always trying to push away from other electrons, spreading out wherever they can.[\[2\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-2) X Research source Advertisement 3. [![Step 3 Understand voltage.](https://www.wikihow.com/images/thumb/7/79/Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg) 3 Understand voltage. [Voltage](https://www.wikihow.com/Test-Voltage-with-a-Multimeter "Test Voltage with a Multimeter") measures the difference in electrical charge between two points.[\[3\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-3) X Research source The greater the difference, the more energetically the two sides attract each other. Here's an example with an everyday battery: - Inside a battery, chemical reactions happen that produces a buildup of electrons. The electrons go to the negative end, while the positive end stays mostly empty. (These are called the negative and positive terminals.) The longer this goes on, the larger the voltage between the two ends. - When you connect a wire between the negative and positive ends, the electrons at the negative end suddenly have somewhere to go. They shoot toward the positive end, creating a current. The larger the voltage, the more electrons move to the positive end each second. 4. [![Step 4 Figure out resistance.](https://www.wikihow.com/images/thumb/5/55/Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg) 4 Figure out resistance. [Resistance](https://www.wikihow.com/Measure-Resistance "Measure Resistance") is exactly what it sounds like. The more resistance something has, the harder it is for the electrons to push through. This slows the current, since fewer electrons can push through each second.[\[4\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-4) X Research source - A resistor is anything in the circuit that adds resistance. You can buy an actual "resistor" at an electronics store, but in a circuits problem it might represent a light bulb or anything else with resistance. 5. [![Step 5 Memorize Ohm's Law.](https://www.wikihow.com/images/thumb/a/a8/Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg) 5 Memorize Ohm's Law. There's a very simple relationship between current, voltage, and resistance.[\[5\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-5) X Research source Write this down or [memorize](https://www.wikihow.com/Improve-Your-Memory "Improve Your Memory") it; you'll use it often when solving circuit problems:[\[6\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-6)X [Expert Source](https://www.wikihow.com/wikiHow:Delivering-a-Trustworthy-Experience) [![Mantas Silvanavicius]()Mantas Silvanavicius Licensed Electrician](https://www.wikihow.com/Author/Mantas-Silvanavicius) Expert Interview - Current = voltage divided by resistance - This is usually written: I = V / R - Think about what happens when you increase V (voltage) or R (resistance). Does this match what you learned in the explanations above? Part 2 Part 2 of 3: ### Calculating Voltage across a Resistor (Series Circuit) [![PDF download](https://www.wikihow.com/extensions/wikihow/socialstamp/images/icon-pdf.svg) Download Article](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) 1. [![Step 1 Understand a series circuit.](https://www.wikihow.com/images/thumb/e/e4/Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg) 1 Understand a series circuit. A [series circuit](https://www.wikihow.com/Solve-a-Series-Circuit "Solve a Series Circuit") is easy to identify. It's just one loop of wire, with everything arranged in a row. The current flows around the entire loop, going through each resistor or element in order. - The current is always the same at any point along the circuit.[\[7\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-7) X Research source - When calculating voltage, it doesn't matter where the resistor is on the circuit. You can pick up the resistors and move them around, and you'll still have the same voltage across each one. - We'll use an example circuit with three resistors in series: R1, R2, and R3. This is powered by a 12 volt battery. We'll find the voltage across each one. 2. [![Step 2 Calculate the total resistance.](https://www.wikihow.com/images/thumb/b/b8/Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg) 2 Calculate the total resistance. Add together all resistance values on the circuit. The answer is the total resistance of the series circuit. - For example, the three resistors R1, R2, and R3 have resistances of 2 Ω (ohms), 3 Ω, and 5 Ω respectively. The total resistance is 2 + 3 + 5 = 10 ohms. 3. [![Step 3 Find the current.](https://www.wikihow.com/images/thumb/5/58/Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg) 3 Find the current. Use Ohm's Law to find the current of the entire circuit. Remember, the current is the same anywhere on a series circuit. Once we calculate the current this way, we can use it for all our calculations.[\[8\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-8) X Research source - Ohm's Law says that the current I = V / R. The voltage across the whole circuit is 12 volts, and the total resistance is 10 ohms. The answer is I = 12 / 10 = 1\.2 amperes . 4. [![Step 4 Adjust Ohm's Law to solve for voltage.](https://www.wikihow.com/images/thumb/8/88/Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg) 4 Adjust Ohm's Law to solve for voltage. With basic [algebra](https://www.wikihow.com/Learn-Algebra "Learn Algebra"), we can change Ohm's Law to solve for voltage instead of current:[\[9\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-9) X Research source - I = V / R - IR = VR / R - IR = V - V = IR 5. [![Step 5 Calculate the voltage across each resistor.](https://www.wikihow.com/images/thumb/d/d1/Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg) 5 Calculate the voltage across each resistor. We know the resistance, we know the current, and we have our equation.[\[10\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-10) X Research source Plug in the numbers and solve. Here's our example problem solved for all three resistors: - Voltage across R1 = V1 = ( 1\.2A )( 2Ω ) = 2.4 volts. - Voltage across R2 = V2 = ( 1\.2A )( 3Ω ) = 3.6 volts. - Voltage across R3 = V3 = ( 1\.2A )( 5Ω ) = 6.0 volts. 6. [![Step 6 Check your answer.](https://www.wikihow.com/images/thumb/4/42/Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg) 6 Check your answer. In a series circuit, the sum of all your answers must equal the total voltage. Add up every voltage you calculated and see if you get the voltage of the entire circuit.[\[11\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-11) X Research source If you didn't, go back and check for mistakes. - In our example, 2.4 + 3.6 + 6.0 = 12 volts, the voltage across the whole circuit. - If your answer is slightly off (for instance, 11.97 instead of 12), you probably rounded a number at some point. Your answer is still correct. - Remember, voltage measures the differences in charge, or numbers of electrons. Imagine counting the number of new electrons you see as you travel along the circuit. If you count them correctly, you're going to end up with the total change in electrons from the beginning to the end. Part 3 Part 3 of 3: ### Calculating Voltage across a Resistor (Parallel Circuit) [![PDF download](https://www.wikihow.com/extensions/wikihow/socialstamp/images/icon-pdf.svg) Download Article](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) 1. [![Step 1 Understand parallel circuits.](https://www.wikihow.com/images/thumb/b/bb/Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg) 1 Understand parallel circuits. Imagine a wire leaving one end of a battery, then splitting into two separate wires. These two wires run [parallel](https://www.wikihow.com/Solve-Parallel-Circuits "Solve Parallel Circuits") to each other, then join up again before they reach the other end of the battery. If there's a resistor on the left wire and a resistor on the right wire, those two resistors are connected "in parallel."[\[12\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-12) X Research source - You can have any number of wires in a parallel circuit. These instructions will still work for a circuit that splits into one hundred wires and comes back together. 2. [![Step 2 Think about how the current flows.](https://www.wikihow.com/images/thumb/c/ce/Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg) 2 Think about how the current flows. In a parallel circuit, the current flows across each path available to it. Current will flow through the wire on the left, cross the left resistor, and reach the other end. At the same time, current will flow through the wire on the right, cross the right resistor, and reach the end. No part of the current doubles back or flows through two parallel resistors. 3. [![Step 3 Use the total voltage to find the voltage across each resistor.](https://www.wikihow.com/images/thumb/d/d7/Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg) 3 Use the total voltage to find the voltage across each resistor. If you know the voltage across the whole circuit, the answer is surprisingly easy. Each parallel wire has the same voltage as the entire circuit.[\[13\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-13) X Research source Let's say a circuit with two parallel resistors is powered by a 6 volt battery. The voltage across the left resistor is 6 volts, and the voltage across the right resistor is 6 volts. It doesn't even matter how much resistance there is. To understand why, think back to the series circuits described above: - Remember that adding voltage drops in a series circuit always results in the total voltage across the circuit. - Think of each path the current takes as a series circuit. The same holds true for this: if you count up all the voltage drops, you'll end up with the total voltage. - Since the current through each of the two wires only passes through one resistor, the voltage across that resistor must equal the total voltage. 4. [![Step 4 Calculate the total current of the circuit.](https://www.wikihow.com/images/thumb/3/3d/Calculate-Voltage-Across-a-Resistor-Step-15.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-15.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-15.jpg) 4 Calculate the total current of the circuit. If the problem doesn't tell you what the total voltage of the circuit is, you'll need to complete a few more steps. Start by finding the total current passing through the circuit.[\[14\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-14) X Research source In a [parallel circuit](https://www.wikihow.com/Make-a-Parallel-Circuit "Make a Parallel Circuit"), the total current is equal to the sum of the current running through each parallel path.[\[15\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-15) X Research source Serway, R.A. and John W. Jewett, Jr., Physics for Scientists and Engineers with Modern Physics. 8th edition. California: Brooks/Cole. 2010. Ebook - In mathematical terms: Itotal = I1 + I2 + I3... - If you're having trouble understanding this, imagine a water pipe split into two paths. The total amount of water flow is just the amount of water flow in each pipe, added together. 5. [![Step 5 Compute the total resistance of the circuit.](https://www.wikihow.com/images/thumb/6/67/Calculate-Voltage-Across-a-Resistor-Step-16.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-16.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-16.jpg) 5 Compute the total resistance of the circuit. Resistors are not as effective in a parallel circuit, because they only block the current going along one wire. In fact, the more wires there are, the easier it is for the current to find a way through. To find the total resistance, solve for Rtotal in this equation:[\[16\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-16) X Research source - 1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3 ... - For example, a circuit has a 2 ohm and a 4 ohm resistor in parallel. 1 / Rtotal = 1/2 + 1/4 = 3/4 → 1 = (3/4)Rtotal → Rtotal = 1/(3/4) = 4/3 = ~1.33 ohms. 6. [![Step 6 Find the voltage from your answers.](https://www.wikihow.com/images/thumb/b/b7/Calculate-Voltage-Across-a-Resistor-Step-17.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-17.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-17.jpg) 6 Find the voltage from your answers. Remember, once we find the total voltage of the circuit, we have found the voltage across any one of the parallel wires. Solve for the whole circuit using Ohm's law.[\[17\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-17) X Research source Here's an example: - A circuit has 5 amperes of current running through it. The total resistance is 1.33 ohms. - According to Ohm's Law, I = V / R, therefore V = IR - V = (5A)(1.33Ω) = 6.65 volts. ## Community Q\&A Search [Add New Question]() - Question What is the percentage of applied voltage that will be dropped across r3=70 if r1=80 and r2=50? ![Community Answer](https://www.wikihow.com/images/thumb/0/0a/CommunityAvatar1.png/-crop-104-104-104px-CommunityAvatar1.png) Community Answer It would be 35%. The higher the resistance, the higher the voltage drop. The ratio of resistances here is 80:50:70. Solving for 70 ohms, we get 35%. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even \$1 helps us in our mission. [Support wikiHow](https://www.wikihow.com/wikiHow:Contribute) [Yes](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [No](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Not Helpful 17](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Helpful 41](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) - Question What is the voltage of a 60 ohm resistor if the circuit voltage is 150 volts with two parallel 30 ohm resistors and one 60 ohm resister in the series? ![Community Answer](https://www.wikihow.com/images/thumb/f/f2/CommunityAvatar3.png/-crop-104-104-104px-CommunityAvatar3.png) Community Answer Assuming you intend to ask what is the voltage drop across the 60 ohm resistor, the answer is 120v. The two parallel 30 ohm resistors have an equivalent resistance of 15 ohms. 1/(1/30 + 1/30) = 15. The total resistance appears as 75 ohms to the 150v source. Find the circuit current by I = E/R or I = 150/75 = 2 amps. Find the voltage drop for the 60 ohm resistor with E = I x R or E = 2 x 60 = 120V drop across the 60 Ohm resistor. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even \$1 helps us in our mission. [Support wikiHow](https://www.wikihow.com/wikiHow:Contribute) [Yes](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [No](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Not Helpful 34](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Helpful 44](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) - Question What becomes the Voltage if we use 2 resistors of 4W in parallel? ![Community Answer](https://www.wikihow.com/images/thumb/0/0a/CommunityAvatar1.png/-crop-104-104-104px-CommunityAvatar1.png) Community Answer As any other data is not provided, the voltage across two resistors of 4w in parallel is the same. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even \$1 helps us in our mission. [Support wikiHow](https://www.wikihow.com/wikiHow:Contribute) [Yes](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [No](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Not Helpful 16](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Helpful 56](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [See more answers](https://www.wikihow.com/Questions/Calculate-Voltage-Across-a-Resistor#offset=3) Ask a Question 200 characters left Include your email address to get a message when this question is answered. [Submit]() Advertisement ## Video ## Tips - The voltage across a resistor is often called a "voltage drop." Thanks [Helpful 5](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Not Helpful 0](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) - If you have a complicated circuit that involves resistors in series and resistors in parallel, pick two nearby resistors. Find the total resistance across them using the rules for resistors in parallel or in series, as appropriate. Now you can treat them as a single resistor. Keep doing this until you have a simple circuit with resistors either in parallel or in series. Thanks [Helpful 0](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Not Helpful 0](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) - Understand the terminology: - Circuit – composed of elements (e.g. resistors, capacitors, and inductors) connected by wires and wherein current can pass through - Resistors – elements that can reduce or resist current - Current – flow of charge into wires; unit: Ampere, A - Voltage – work done per unit charge; unit: Voltage, V - Resistance – measurement of the opposition of an element to electric current; unit: Ohm, Ω Thanks [Helpful 0](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [Not Helpful 0](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) Submit a Tip All tip submissions are carefully reviewed before being published Name Please provide your name and last initial [Submit](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) Thanks for submitting a tip for review\! 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[↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-1) Serway, R.A. and John W. Jewett, Jr., Physics for Scientists and Engineers with Modern Physics. 8th edition. California: Brooks/Cole. 2010. Ebook 2. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-2) <https://energyeducation.ca/encyclopedia/Electric_charge> 3. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-3) <https://www.education.vic.gov.au/school/teachers/teachingresources/discipline/science/continuum/Pages/voltage.aspx> 4. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-4) <https://www.physicsclassroom.com/class/circuits/Lesson-3/Resistance> 5. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-5) <https://phet.colorado.edu/en/simulations/ohms-law> 6. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-6) Mantas Silvanavicius. Licensed Electrician. Expert Interview 7. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-7) <https://energyeducation.ca/encyclopedia/Series_circuit> 8. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-8) <https://www.calculator.net/ohms-law-calculator.html> 9. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-9) <https://www.hsa.org.uk/electricity/current-voltage-and-resistance> [More References (8)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#aiinfo) 1. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-10) <https://pressbooks.bccampus.ca/collegephysics/chapter/resistors-in-series-and-parallel/> 2. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-11) <https://pressbooks.bccampus.ca/collegephysics/chapter/resistors-in-series-and-parallel/> 3. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-12) <https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/simple-parallel-circuits/> 4. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-13) <https://www.physicsclassroom.com/class/circuits/Lesson-4/Parallel-Circuits> 5. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-14) <https://pressbooks.bccampus.ca/basicelectricity/chapter/ground/> 6. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-15) Serway, R.A. and John W. Jewett, Jr., Physics for Scientists and Engineers with Modern Physics. 8th edition. California: Brooks/Cole. 2010. Ebook 7. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-16) [https://phys.libretexts.org/Bookshelves/University\_Physics/University\_Physics\_(OpenStax)/University\_Physics\_II\_-\_Thermodynamics\_Electricity\_and\_Magnetism\_(OpenStax)/10%3A\_Direct-Current\_Circuits/10.03%3A\_Resistors\_in\_Series\_and\_Parallel](https://phys.libretexts.org/Bookshelves/University_Physics/University_Physics_$OpenStax$/University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_$OpenStax$/10%3A_Direct-Current_Circuits/10.03%3A_Resistors_in_Series_and_Parallel) 8. [↑](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_ref-17) [https://phys.libretexts.org/Bookshelves/University\_Physics/University\_Physics\_(OpenStax)/University\_Physics\_II\_-\_Thermodynamics\_Electricity\_and\_Magnetism\_(OpenStax)/10%3A\_Direct-Current\_Circuits/10.03%3A\_Resistors\_in\_Series\_and\_Parallel](https://phys.libretexts.org/Bookshelves/University_Physics/University_Physics_$OpenStax$/University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_$OpenStax$/10%3A_Direct-Current_Circuits/10.03%3A_Resistors_in_Series_and_Parallel) ## About This Article MS Co-authored by: [Mantas Silvanavicius](https://www.wikihow.com/Author/Mantas-Silvanavicius) Licensed Electrician This article was co-authored by [Mantas Silvanavicius](https://www.wikihow.com/Author/Mantas-Silvanavicius). Mantas Silvanavicius is a Licensed Electrician and the Owner of M+S Electric based in Las Vegas, Nevada. With more than 20 years of experience, he specializes in home electrical installations, testing, and wiring. Mantas and his team have completed projects for companies such as Seiko and Springhill Suites by Marriott. M+S Electric is licensed, bonded, and insured. This article has been viewed 1,032,909 times. 27 votes - 81% Co-authors: 13 Updated: September 7, 2024 Views: 1,032,909 Categories: [Electromagnetism](https://www.wikihow.com/Category:Electromagnetism "Category:Electromagnetism") [Article SummaryX](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#summary_wrapper) To calculate voltage across a resistor in a series circuit, start by adding together all of the resistance values in the circuit. Then, divide the voltage across the circuit by the total resistance to find the current. Once you have the current, calculate voltage for the individual resistors by multiplying the current by the resistance. For example, in a series circuit with 3 resistors of 2, 3 and 5 Ohms, and a voltage of 12 volts, the current would be 12 divided by 10, or 1.2 amperes. For the 2 Ohm resistor, the voltage would be 1.2 times 2, or 2.4 volts. If you want to learn how to calculate voltage in a parallel circuit, keep reading the article\! Did this summary help you? 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MS Co-authored by: [Mantas Silvanavicius](https://www.wikihow.com/Author/Mantas-Silvanavicius) Licensed Electrician Co-authors: 13 Updated: September 7, 2024 Views: 1,032,909 81% of readers found this article helpful. 27 votes - 81% Click a star to add your vote ![Mohd Rodzi Mohamad](https://www.wikihow.com/images/thumb/f/f5/CommunityAvatar4.png/-crop-72-72-72px-CommunityAvatar4.png) Mohd Rodzi Mohamad Aug 26, 2016 "This article is very neatly and clearly explained with illustrations of pictures for better comprehension. Very helpful for electronic and electrical students, technicians and even hobbyists. Simple vocabulary makes it easy to follow, too. Thank you."..." [more](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) ![Sachintha Kolugala](https://www.wikihow.com/images/thumb/f/f2/CommunityAvatar3.png/-crop-72-72-72px-CommunityAvatar3.png) Sachintha Kolugala May 17, 2016 "I was lost in currents and voltages. But this article really helped me to take it in easier way. Educational articles can only give us the details, but this is so encouraging. Thank you, wikiHow!"..." [more](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) ![Ale C.](https://www.wikihow.com/images/thumb/0/0a/CommunityAvatar1.png/-crop-72-72-72px-CommunityAvatar1.png) Ale C. Oct 4, 2016 "This wikiHow article summarized multiple wordy textbook pages into a few slides with visual and text explanations. Thank you for the extremely helpful article. "..." [more](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) ![John Rodrigues](https://www.wikihow.com/images/thumb/f/f5/CommunityAvatar4.png/-crop-72-72-72px-CommunityAvatar4.png) John Rodrigues Sep 14, 2017 "The part where it is explained very well how to calculate voltage drop across each resistor connected in series where the resistance and the current is known."..." 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Readable Markdown	[![PDF download](https://www.wikihow.com/extensions/wikihow/socialstamp/images/icon-pdf.svg) Download Article](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) [![PDF download](https://www.wikihow.com/extensions/wikihow/socialstamp/images/icon-pdf.svg) Download Article](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor) Before you can calculate the voltage across a resistor, you'll first have to determine what kind of circuit you are using. If you need a review of the basic terms or a little help understanding [circuits](https://www.wikihow.com/Make-a-Simple-Electrical-Circuit "Make a Simple Electrical Circuit"), start with the first section. Otherwise, jump ahead to the type of circuit you have to solve. 1. [![Step 1 Learn about current.](https://www.wikihow.com/images/thumb/2/2b/Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-1-Version-2.jpg) Let’s think about current by using an analogy: imagine you pour a bag of corn kernels into a bowl. Each corn kernel is an [electron](https://www.wikihow.com/Find-Electrons "Find Electrons"), and the stream of kernels flowing into the bowl is the current.[\[1\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-1) When talking about the flow, you describe it by saying how many kernels are flowing each second. When talking about a current, you measure it in amperes ([amps](https://www.wikihow.com/Find-Amps "Find Amps")), or a certain (very large) number of electrons flowing per second. 2. [![Step 2 Think about electrical charge.](https://www.wikihow.com/images/thumb/a/a1/Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-2-Version-2.jpg) Electrons have a "negative" electrical charge. This means they attract (or flow toward) objects with a positive charge, and repel (or flow away from) objects with a negative charge. Since they're all negative, electrons are always trying to push away from other electrons, spreading out wherever they can.[\[2\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-2) Advertisement 3. [![Step 3 Understand voltage.](https://www.wikihow.com/images/thumb/7/79/Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-3-Version-2.jpg) [Voltage](https://www.wikihow.com/Test-Voltage-with-a-Multimeter "Test Voltage with a Multimeter") measures the difference in electrical charge between two points.[\[3\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-3) The greater the difference, the more energetically the two sides attract each other. Here's an example with an everyday battery: - Inside a battery, chemical reactions happen that produces a buildup of electrons. The electrons go to the negative end, while the positive end stays mostly empty. (These are called the negative and positive terminals.) The longer this goes on, the larger the voltage between the two ends. - When you connect a wire between the negative and positive ends, the electrons at the negative end suddenly have somewhere to go. They shoot toward the positive end, creating a current. The larger the voltage, the more electrons move to the positive end each second. 4. [![Step 4 Figure out resistance.](https://www.wikihow.com/images/thumb/5/55/Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-4-Version-2.jpg) [Resistance](https://www.wikihow.com/Measure-Resistance "Measure Resistance") is exactly what it sounds like. The more resistance something has, the harder it is for the electrons to push through. This slows the current, since fewer electrons can push through each second.[\[4\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-4) - A resistor is anything in the circuit that adds resistance. You can buy an actual "resistor" at an electronics store, but in a circuits problem it might represent a light bulb or anything else with resistance. 5. [![Step 5 Memorize Ohm's Law.](https://www.wikihow.com/images/thumb/a/a8/Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-5-Version-2.jpg) There's a very simple relationship between current, voltage, and resistance.[\[5\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-5) Write this down or [memorize](https://www.wikihow.com/Improve-Your-Memory "Improve Your Memory") it; you'll use it often when solving circuit problems:[\[6\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-6) - Current = voltage divided by resistance - This is usually written: I = V / R - Think about what happens when you increase V (voltage) or R (resistance). Does this match what you learned in the explanations above? 1. [![Step 1 Understand a series circuit.](https://www.wikihow.com/images/thumb/e/e4/Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-6-Version-2.jpg) A [series circuit](https://www.wikihow.com/Solve-a-Series-Circuit "Solve a Series Circuit") is easy to identify. It's just one loop of wire, with everything arranged in a row. The current flows around the entire loop, going through each resistor or element in order. - The current is always the same at any point along the circuit.[\[7\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-7) - When calculating voltage, it doesn't matter where the resistor is on the circuit. You can pick up the resistors and move them around, and you'll still have the same voltage across each one. - We'll use an example circuit with three resistors in series: R1, R2, and R3. This is powered by a 12 volt battery. We'll find the voltage across each one. 2. [![Step 2 Calculate the total resistance.](https://www.wikihow.com/images/thumb/b/b8/Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-7-Version-2.jpg) Add together all resistance values on the circuit. The answer is the total resistance of the series circuit. - For example, the three resistors R1, R2, and R3 have resistances of 2 Ω (ohms), 3 Ω, and 5 Ω respectively. The total resistance is 2 + 3 + 5 = 10 ohms. 3. [![Step 3 Find the current.](https://www.wikihow.com/images/thumb/5/58/Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-8-Version-2.jpg) Use Ohm's Law to find the current of the entire circuit. Remember, the current is the same anywhere on a series circuit. Once we calculate the current this way, we can use it for all our calculations.[\[8\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-8) - Ohm's Law says that the current I = V / R. The voltage across the whole circuit is 12 volts, and the total resistance is 10 ohms. The answer is I = 12 / 10 = 1\.2 amperes. 4. [![Step 4 Adjust Ohm's Law to solve for voltage.](https://www.wikihow.com/images/thumb/8/88/Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-9-Version-2.jpg) With basic [algebra](https://www.wikihow.com/Learn-Algebra "Learn Algebra"), we can change Ohm's Law to solve for voltage instead of current:[\[9\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-9) - I = V / R - IR = VR / R - IR = V - V = IR 5. [![Step 5 Calculate the voltage across each resistor.](https://www.wikihow.com/images/thumb/d/d1/Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-10-Version-2.jpg) We know the resistance, we know the current, and we have our equation.[\[10\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-10) Plug in the numbers and solve. Here's our example problem solved for all three resistors: - Voltage across R1 = V1 = (1\.2A)(2Ω) = 2.4 volts. - Voltage across R2 = V2 = (1\.2A)(3Ω) = 3.6 volts. - Voltage across R3 = V3 = (1\.2A)(5Ω) = 6.0 volts. 6. [![Step 6 Check your answer.](https://www.wikihow.com/images/thumb/4/42/Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-11-Version-2.jpg) In a series circuit, the sum of all your answers must equal the total voltage. Add up every voltage you calculated and see if you get the voltage of the entire circuit.[\[11\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-11) If you didn't, go back and check for mistakes. - In our example, 2.4 + 3.6 + 6.0 = 12 volts, the voltage across the whole circuit. - If your answer is slightly off (for instance, 11.97 instead of 12), you probably rounded a number at some point. Your answer is still correct. - Remember, voltage measures the differences in charge, or numbers of electrons. Imagine counting the number of new electrons you see as you travel along the circuit. If you count them correctly, you're going to end up with the total change in electrons from the beginning to the end. 1. [![Step 1 Understand parallel circuits.](https://www.wikihow.com/images/thumb/b/bb/Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-12-Version-2.jpg) Imagine a wire leaving one end of a battery, then splitting into two separate wires. These two wires run [parallel](https://www.wikihow.com/Solve-Parallel-Circuits "Solve Parallel Circuits") to each other, then join up again before they reach the other end of the battery. If there's a resistor on the left wire and a resistor on the right wire, those two resistors are connected "in parallel."[\[12\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-12) - You can have any number of wires in a parallel circuit. These instructions will still work for a circuit that splits into one hundred wires and comes back together. 2. [![Step 2 Think about how the current flows.](https://www.wikihow.com/images/thumb/c/ce/Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-13-Version-2.jpg) In a parallel circuit, the current flows across each path available to it. Current will flow through the wire on the left, cross the left resistor, and reach the other end. At the same time, current will flow through the wire on the right, cross the right resistor, and reach the end. No part of the current doubles back or flows through two parallel resistors. 3. [![Step 3 Use the total voltage to find the voltage across each resistor.](https://www.wikihow.com/images/thumb/d/d7/Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-14-Version-2.jpg) If you know the voltage across the whole circuit, the answer is surprisingly easy. Each parallel wire has the same voltage as the entire circuit.[\[13\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-13) Let's say a circuit with two parallel resistors is powered by a 6 volt battery. The voltage across the left resistor is 6 volts, and the voltage across the right resistor is 6 volts. It doesn't even matter how much resistance there is. To understand why, think back to the series circuits described above: - Remember that adding voltage drops in a series circuit always results in the total voltage across the circuit. - Think of each path the current takes as a series circuit. The same holds true for this: if you count up all the voltage drops, you'll end up with the total voltage. - Since the current through each of the two wires only passes through one resistor, the voltage across that resistor must equal the total voltage. 4. [![Step 4 Calculate the total current of the circuit.](https://www.wikihow.com/images/thumb/3/3d/Calculate-Voltage-Across-a-Resistor-Step-15.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-15.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-15.jpg) If the problem doesn't tell you what the total voltage of the circuit is, you'll need to complete a few more steps. Start by finding the total current passing through the circuit.[\[14\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-14) In a [parallel circuit](https://www.wikihow.com/Make-a-Parallel-Circuit "Make a Parallel Circuit"), the total current is equal to the sum of the current running through each parallel path.[\[15\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-15) - In mathematical terms: Itotal = I1 + I2 + I3... - If you're having trouble understanding this, imagine a water pipe split into two paths. The total amount of water flow is just the amount of water flow in each pipe, added together. 5. [![Step 5 Compute the total resistance of the circuit.](https://www.wikihow.com/images/thumb/6/67/Calculate-Voltage-Across-a-Resistor-Step-16.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-16.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-16.jpg) Resistors are not as effective in a parallel circuit, because they only block the current going along one wire. In fact, the more wires there are, the easier it is for the current to find a way through. To find the total resistance, solve for Rtotal in this equation:[\[16\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-16) - 1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3 ... - For example, a circuit has a 2 ohm and a 4 ohm resistor in parallel. 1 / Rtotal = 1/2 + 1/4 = 3/4 → 1 = (3/4)Rtotal → Rtotal = 1/(3/4) = 4/3 = ~1.33 ohms. 6. [![Step 6 Find the voltage from your answers.](https://www.wikihow.com/images/thumb/b/b7/Calculate-Voltage-Across-a-Resistor-Step-17.jpg/v4-460px-Calculate-Voltage-Across-a-Resistor-Step-17.jpg)](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#/Image:Calculate-Voltage-Across-a-Resistor-Step-17.jpg) Remember, once we find the total voltage of the circuit, we have found the voltage across any one of the parallel wires. Solve for the whole circuit using Ohm's law.[\[17\]](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#_note-17) Here's an example: - A circuit has 5 amperes of current running through it. The total resistance is 1.33 ohms. - According to Ohm's Law, I = V / R, therefore V = IR - V = (5A)(1.33Ω) = 6.65 volts. Search [Add New Question]() - Question What is the percentage of applied voltage that will be dropped across r3=70 if r1=80 and r2=50? ![Community Answer](https://www.wikihow.com/images/thumb/0/0a/CommunityAvatar1.png/-crop-104-104-104px-CommunityAvatar1.png) Community Answer It would be 35%. The higher the resistance, the higher the voltage drop. The ratio of resistances here is 80:50:70. Solving for 70 ohms, we get 35%. - Question What is the voltage of a 60 ohm resistor if the circuit voltage is 150 volts with two parallel 30 ohm resistors and one 60 ohm resister in the series? ![Community Answer](https://www.wikihow.com/images/thumb/f/f2/CommunityAvatar3.png/-crop-104-104-104px-CommunityAvatar3.png) Community Answer Assuming you intend to ask what is the voltage drop across the 60 ohm resistor, the answer is 120v. The two parallel 30 ohm resistors have an equivalent resistance of 15 ohms. 1/(1/30 + 1/30) = 15. The total resistance appears as 75 ohms to the 150v source. Find the circuit current by I = E/R or I = 150/75 = 2 amps. Find the voltage drop for the 60 ohm resistor with E = I x R or E = 2 x 60 = 120V drop across the 60 Ohm resistor. - Question What becomes the Voltage if we use 2 resistors of 4W in parallel? ![Community Answer](https://www.wikihow.com/images/thumb/0/0a/CommunityAvatar1.png/-crop-104-104-104px-CommunityAvatar1.png) Community Answer As any other data is not provided, the voltage across two resistors of 4w in parallel is the same. [See more answers](https://www.wikihow.com/Questions/Calculate-Voltage-Across-a-Resistor#offset=3) Ask a Question 200 characters left Include your email address to get a message when this question is answered. [Submit]() Advertisement ## Video - The voltage across a resistor is often called a "voltage drop." Thanks - If you have a complicated circuit that involves resistors in series and resistors in parallel, pick two nearby resistors. Find the total resistance across them using the rules for resistors in parallel or in series, as appropriate. Now you can treat them as a single resistor. Keep doing this until you have a simple circuit with resistors either in parallel or in series. Thanks - Understand the terminology: - Circuit – composed of elements (e.g. resistors, capacitors, and inductors) connected by wires and wherein current can pass through - Resistors – elements that can reduce or resist current - Current – flow of charge into wires; unit: Ampere, A - Voltage – work done per unit charge; unit: Voltage, V - Resistance – measurement of the opposition of an element to electric current; unit: Ohm, Ω Thanks Thanks for submitting a tip for review\! Advertisement ## References About This Article [Article SummaryX](https://www.wikihow.com/Calculate-Voltage-Across-a-Resistor#summary_wrapper) To calculate voltage across a resistor in a series circuit, start by adding together all of the resistance values in the circuit. Then, divide the voltage across the circuit by the total resistance to find the current. Once you have the current, calculate voltage for the individual resistors by multiplying the current by the resistance. For example, in a series circuit with 3 resistors of 2, 3 and 5 Ohms, and a voltage of 12 volts, the current would be 12 divided by 10, or 1.2 amperes. For the 2 Ohm resistor, the voltage would be 1.2 times 2, or 2.4 volts. If you want to learn how to calculate voltage in a parallel circuit, keep reading the article\! Did this summary help you? Thanks to all authors for creating a page that has been read 1,032,909 times. 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