Watt to Amp Calculator
Convert watts to amps, or amps to watts, for DC, single-phase AC and three-phase AC, with the power factor included.
To convert watts to amps, divide the watts by the volts: a 1,500 W heater on a 120 V circuit draws 12.5 A. For AC with a power factor below 1, divide by the volts times the power factor, and for three-phase also divide by the square root of 3 (about 1.732), using the line-to-line voltage.
This calculator is for estimates and learning, and it is not a substitute for a device's nameplate, a data sheet or a licensed electrician. It assumes steady RMS values and, for three-phase, a balanced load, and it does not size wire or breakers or apply any electrical code.
Current
12.5 A
- Real power
- 1,500 W = 1.5 kW
- Current
- 12.5 A
- Voltage
- 120 V
- Apparent power
- 1,500 VA
- Power factor
- 1
Single-phase: watts = volts x amps x power factor. Shown to 4 significant figures.
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About the Watt to Amp Calculator
Watts measure the power a device uses, amps the current it draws, and volts the push behind that current; one watt is one volt times one amp. In a DC circuit, or for an AC load like a heater or an incandescent bulb, watts are simply volts times amps, so amps are watts divided by volts. Motors, compressors and some power supplies are different: their current runs slightly out of step with the voltage, so they draw more amps than the watts alone suggest. The power factor captures that, as the fraction of power actually delivered compared with the same volts and amps in step. A 1,200 W load at 120 V with a power factor of 0.8 draws 12.5 A, the same current as a 1,500 W heater, and its apparent power is 1,500 VA. Three-phase systems share the load across three wires, so the formula adds the square root of 3: 10 kW at 400 V line-to-line with a power factor of 0.85 draws 16.98 A in each line.
Frequently asked questions
How many amps is 1,500 watts?+
At 120 V, 1,500 / 120 = 12.5 A. At 240 V it is half that, 6.25 A. The higher the voltage, the fewer amps the same power needs.
What power factor should I use?+
Use 1 for resistive loads such as heaters, kettles and incandescent bulbs. Motors run lower: the example motor in the U.S. Department of Energy fact sheet uses 0.763. A nameplate or data sheet may list the figure. If you do not know it, 1 gives the smallest possible current, so the real draw may be higher.
What is the three-phase formula?+
Watts = volts x amps x power factor x 1.732, where the volts are line-to-line and the amps are the current in each line, for a balanced load. The Department of Energy fact sheet applies it to a motor at 469.7 V and 37 A with a power factor of 0.763, which works out to about 22,970 W, or 22.97 kW.
Can I convert amps to watts too?+
Yes. Choose Amps to watts and the watt to amp conversion runs the other way, multiplying instead: 15 A at 240 V with a power factor of 1 is 3,600 W.
Power as P = IV, with 1 A x V = 1 W: OpenStax, College Physics 2e, section 20.4. Three-phase power as V x I x PF x the square root of 3 with line-to-line volts, the power factor definition and the 469.7 V, 37 A, 0.763 motor example: U.S. Department of Energy, Motor Challenge fact sheet Determining Electric Motor Load and Efficiency, Equation 1.
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