Amps to Watts Calculator

Why convert amps to watts

A clamp meter reads current. Breakers, appliance labels, generators, and electricity bills all talk in watts. To connect a measured amp reading to any of those, you multiply by the voltage — and for AC motor or electronic loads, by the power factor as well.

The distinction that trips people up is real power versus apparent power. Voltage times current gives apparent power in volt-amps (VA), which is what the wiring physically carries. Only the portion of that current in step with the voltage does work; the power factor is the fraction that counts. Watts is apparent power times power factor, and watts is what actually heats, spins, and gets billed.

The amps to watts formula

Single-phase AC:

Three-phase, using line-to-line voltage:

is real power in watts, is voltage, is current in amps, and is the power factor from 0 to 1. For DC or a resistive AC load, and it’s just .

Worked example

The calculator’s defaults describe a single-phase load: 10 A at 120 V with a power factor of 0.8.

Apparent power first:

Then scale by the power factor:

The load consumes 960 watts. The other 240 VA is reactive — carried by the wire, tracked by no meter. If the load were resistive, the power factor would be 1 and all 1,200 VA would be 1,200 W of real power.

Amps to Watts Calculator worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

Three-phase worked example

A three-phase load pulling 15 A per line at 208 V line-to-line, power factor 0.85:

Amps to watts reference

Resistive load, power factor 1:

Current	12 V	120 V	240 V
1 A	12 W	120 W	240 W
5 A	60 W	600 W	1,200 W
10 A	120 W	1,200 W	2,400 W
15 A	180 W	1,800 W	3,600 W
20 A	240 W	2,400 W	4,800 W

For a motor or non-corrected electronic load, multiply the table figure by the power factor. A 15 A motor on 240 V at power factor 0.85 delivers about 3,060 W, not 3,600 W.

What the result tells you

The watts figure is the real power at the moment the current was measured — not necessarily the load’s rated wattage, since motors, heaters mid-cycle, and dimmed lights all draw less than their nameplate. For wire and breaker sizing, the apparent power (volts × amps, before the power-factor step) is the figure that matters, because that’s the current the conductors actually carry.

Common mistakes

Calling volts × amps “watts.” That’s VA. Real power is lower by the power factor for any reactive load.
Assuming power factor 1 for a motor. It overstates the wattage and hides how much current the circuit is really carrying.
Using the wrong voltage. A 240 V appliance metered as 120 V halves the calculated power.
Forgetting √3 for three-phase, or using phase voltage where line-to-line voltage belongs.

For the reverse, use the watts to amps calculator. If you know resistance instead of voltage, volts to amps applies Ohm’s law, and for kilowatt totals see amps to kilowatts.

About the formula: Use the stated electrical relationship and enter values in the displayed units.

Frequently Asked Questions

How many watts is 10 amps?+

You can't say without the voltage. At 120 V and a power factor of 1, 10 A is 1,200 W. At 240 V it's 2,400 W. At 12 V DC it's 120 W. Current alone doesn't set power — voltage does most of the work in the formula.

How does this amps to watts calculation work?+

Real power is current times voltage, then scaled by the power factor and, for three-phase, by √3. The power factor is in there because not all the current in an AC circuit does useful work — some of it just cycles in and out of a magnetic field.

What power factor should a household appliance use?+

Resistive loads — toasters, kettles, space heaters, incandescent bulbs — run at 1.0. Refrigerators, well pumps, power tools, and anything with a motor or compressor usually sit between 0.7 and 0.9. Use the nameplate figure when the appliance gives one.

Why is real power lower than voltage times a clamp-meter reading?+

Multiplying voltage by a measured current gives apparent power in volt-amps, not watts. Real power is that figure times the power factor, so it's equal to or less than the VA number. The difference is reactive power, which loads the wiring but does no work.

Does this work for a 12V DC car or battery circuit?+

Yes. Set the voltage to 12 (or your actual battery voltage) and leave power factor at 1, since DC has no power factor. A device drawing 5 A from a 12 V battery is using 60 W.

How do I convert amps to watts for a three-phase motor?+

Choose the three-phase system option, enter the line current and the line-to-line voltage, and set the power factor from the motor nameplate — typically 0.85 to 0.9 at full load. The calculator applies the √3 factor for you.