Voltage Calculator

Use the voltage calculator below to calculate the voltage given the current, power, or resistance.

Calculation Formulas:

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How to Calculate Voltage From Power and Resistance

Voltage is the potential difference between two points in an electrical circuit, measured in volts. In a static electric field, it is the measure of the work needed to move a unit of electric charge between two points.

You can calculate the voltage in a circuit using Ohm’s Law, which states that the current through a circuit element is directly proportional to the potential difference applied to it and inversely proportional to the resistance.[1]

Voltage Formula

The Ohm’s Law formula states I = V/R, where I is the current through the circuit (in amperes or amps), V is the potential difference across the circuit (in volts), and R is the resistance of the circuit (in ohms).[2]

By rearranging this formula, you can calculate the voltage by multiplying the current flowing through a circuit by the resistance of the circuit. The formula to calculate voltage is:

V = I × R

Thus, the voltage (or potential difference) V across the circuit is equal to the product of the current I flowing through the circuit and the resistance R of the circuit.

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This is the formula that is used to convert amps to volts.

How to Calculate the Voltage From Power

You can also calculate the voltage in a circuit using Watt’s Law power formula. If you know the power in watts drawn through a circuit and the current in amps, the formula to calculate the voltage is:

V = P / I

The voltage (or potential difference across) V of the circuit is equal to the power P drawn through the circuit divided by the current I flowing through the circuit.

This is the formula that is used to convert watts to volts.


  1. Brandon Mitchell, Robert Ekey, Roy McCullough, and William Reitz, A Fan-tastic Quantitative Exploration of Ohm’s Law, https://aapt.scitation.org/doi/full/10.1119/1.5021431
  2. National Institute of Standards and Technology, Ampere: The Present, https://www.nist.gov/si-redefinition/ampere-present