Watts to Amps Calculator

Convert watts to amps or amps to watts for DC, single-phase and three-phase circuits, with power factor.

Formula explained below

Convert
Circuit

From 0 to 1. Use 1 if you do not know it.

Result

15.000 amps

Power
1,800.0 W
Apparent power (kVA)
1.8

1,800 W at 120 V draws about 15 A.

Calculation breakdown

StepFormulaResult
Current1,800 W ÷ (120 V × 1)15.0000 A

How it works

Choose whether to convert watts to amps or amps to watts, the circuit type, and enter the voltage. For AC circuits, enter the power factor.

DC: Amps = Watts ÷ VoltsAC single-phase: Amps = Watts ÷ (Volts × Power factor)AC three-phase: Amps = Watts ÷ (√3 × Volts × Power factor)Watts = Amps × Volts (× Power factor for AC; × √3 as well for three-phase)

Worked example

A 1,800 W load on a 120 V single-phase circuit with a power factor of 0.9:

  1. Apparent power: 1,800 ÷ 0.9 = 2,000 VA
  2. Current: 1,800 ÷ (120 × 0.9) = 16.67 A

At a power factor of 1 the same load draws 1,800 ÷ 120 = 15 A.

Rounding

Amps are shown to three decimal places and watts to one. Calculations use the unrounded values.

Sources

Frequently asked questions

How do you convert watts to amps?

For a DC circuit, divide the watts by the volts. A 1,800 watt load on 120 volts draws 1,800 ÷ 120 = 15 amps. A watt is the power of one ampere under one volt, which NIST gives as the definition.

How do you convert amps to watts?

Multiply the amps by the volts. 15 amps at 120 volts is 1,800 watts. For AC circuits also multiply by the power factor, which is 1 for a purely resistive load such as a heater.

What is power factor?

Power factor is the share of the apparent power that does useful work in an AC circuit, a number from 0 to 1. Motors and some electronics have a power factor below 1, so they draw more current for the same watts. The calculator starts at 1.

What is the three-phase formula?

For a balanced three-phase circuit, amps equal watts divided by the square root of 3 times the line-to-line voltage times the power factor. For 10,000 watts at 400 volts and a power factor of 0.8 that is about 18.04 amps.

Can I use this to size a breaker or wire?

No. This only converts between watts and amps. Sizing a breaker or wire involves electrical code rules, continuous loads and conditions that this calculator does not cover. Ask a licensed electrician.

Watt-HourBattery energy and runtimeAC SizeBTU for a room air conditionerPercentagePercentage of, change & differenceFractionAdd, subtract and simplify

For information only. Do not use this to size breakers or wiring. Electrical work should be checked by a licensed electrician.