# How To Find Resistance With Power & Voltage

Most electrical calculations involving resistance, voltage, current or power are solved using Ohm's law. Ohm's law, discovered in 1827 by Georg Simon Ohm, states that the current in a conductor is proportional to the voltage and inversely proportional to the resistance. Since power, measured in watts, is a function of voltage and current, and current is a function of voltage and resistance, it is possible to calculate resistance from power and voltage. The calculations are simple but an understanding of simple math is advantageous.

### Step 1

Enter the power, in watts, into the calculator. Divide the wattage by the voltage. The result is the current because Ohm's law states that current = power / voltage. Record the current value for later use. For example if the power is 100 watts and the voltage is 50 volts, the current is 100 / 50, or 2 amps.

### Step 2

Calculate the resistance, in Ohms, by dividing the voltage by the current. Ohms law states that voltage = current x resistance, so by rearranging the formula resistance = voltage / current. Using the example in Step 1, with a voltage of 50 volts and a current of 2 amps, the resistance is 50 / 2, or 25 ohms.

### Step 3

Check for errors in the calculation. Divide the voltage squared (voltage x voltage) by the calculated resistance. If the result does not equal the power, in watts, there was an error in the calculations.

### TL;DR (Too Long; Didn't Read)

Use an online calculator to simplify the Ohms law calculations.

Ohms law states that V=IR, where "V" is voltage, "I" is current and "R" is resistance. If you can remember that Ohms law is a "Very Important Rule," you have remembered V, I and R in the correct order.

## Warning

Always double-check your results before applying the values to an electrical project. Using incorrect values may result in fire, electric shock and death.

### Cite This Article

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Robinson, David. "How To Find Resistance With Power & Voltage" *sciencing.com*, https://www.sciencing.com/resistance-power-voltage-8238550/. 24 April 2017.

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Robinson, David. (2017, April 24). How To Find Resistance With Power & Voltage. *sciencing.com*. Retrieved from https://www.sciencing.com/resistance-power-voltage-8238550/

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Robinson, David. How To Find Resistance With Power & Voltage last modified March 24, 2022. https://www.sciencing.com/resistance-power-voltage-8238550/