Watts to Volts Calculator

What is a watts to volts calculator?

A watts to volts calculator works out the voltage of a circuit, measured in volts, from the electrical power it consumes in watts and the current that flows through it in amps. Power describes how much energy a device uses each second, current describes how much charge moves through the conductor, and voltage describes the electrical “pressure” that pushes that charge along. When you already know the power rating and the measured current, this tool gives you the voltage without any manual arithmetic.

How does it work?

Electrical power is the product of voltage and current, so $P = V \times I$. Rearranging that relationship to solve for voltage gives the formula used by this calculator:

where $V$ is the voltage in volts (V), $P$ is the power in watts (W), and $I$ is the current in amps (A). The current must be greater than zero, because dividing by zero is undefined, and a circuit with no current does not have a voltage you can recover from power alone.

How to use the calculator

1. Enter the power of the device in watts.
2. Enter the current flowing through the circuit in amps.
3. The calculator instantly shows the voltage in volts. The result appears only when both values are present and the current is not zero.

Worked examples

Suppose a load draws 120 watts while carrying a current of 10 amps. The voltage across it is:

A more powerful load rated at 1000 watts that carries 5 amps sits at a higher voltage:

For a small device using just 60 watts at a low current of 0.5 amps, the voltage is:

Practical notes

This relationship holds directly for DC circuits and for purely resistive AC loads. For reactive AC loads such as motors and transformers, the power factor also matters, and the voltage becomes volts = watts ÷ (amps × power factor). If instead you know the voltage and want the current, use the watts to amps calculator at https://www.mega-calculator.com/physics/watts-to-amps/, and to go the other way and find power from voltage and current, the volts to watts calculator at https://www.mega-calculator.com/physics/volts-to-watts/ does the multiplication for you.

FAQ

Why does the result disappear when I enter 0 amps?

Dividing power by zero current has no meaningful answer, so the calculator hides the result until you enter a current greater than zero.

Can I use this for AC power?

Yes for purely resistive AC loads. For reactive loads you must include the power factor, otherwise the computed voltage will be too low compared with the true RMS voltage.