Watts to Volts Calculator

How to use the watts to volts calculator

Enter the power and the current, and you get the voltage — volts = watts ÷ amps. This is the least-asked of the three power directions, and honestly so: you usually already know your supply voltage. It earns a place for the one case where you don’t — backing out an unknown supply from a measured load.

You’d actually reach for it to confirm a supply: you measure a device pulling 600 W at 5 A and want to check the outlet is really 120 V, or you’re reverse-engineering an unlabeled adapter or DC system from meter readings. It’s also the third corner of the W = V × A triangle — when you know the watts and the amps, this gives the volts.

The math is volts = watts ÷ amps, exact for DC and resistive loads. For AC motors there’s a catch: real power (watts) is less than apparent power (volt-amps) by the power factor, so dividing watts by amps understates the voltage. For those, divide the volt-amps (VA) by the current instead; for resistive loads the two are the same.

The triangle is the thing to hold onto: watts, volts, and amps lock together as W = V × A, so any two give the third. This tool is the volts corner; the watts-to-amps and volts-to-watts (or amps-to-watts) tools cover the others. They’re the same relationship rearranged, picked by which quantity you’re missing.

In practice this is a verification and diagnosis tool more than a sizing one — your supply is almost always a known 120 or 240 (or 12 for automotive). If the result doesn’t land near a standard voltage, that’s a signal: suspect a power-factor effect (an AC motor) or a measurement error rather than an exotic supply.

The formula

Voltage is power divided by current, exact for DC and resistive loads:

volts = watts ÷ amps

Worked example with the defaults — 600 W ÷ 5 A = 120 V. A 1,200 W load at 10 A is also 120 V; a 60 W load at 5 A is 12 V.

For AC motors, divide volt-amps (VA), not watts, by the current — real power is less than VA by the power factor, so using watts understates the voltage. For resistive loads the two are identical.

Frequently asked questions