Watts to amps calculator
Enter the watts and the voltage. You get the amps, for DC, single-phase or three-phase power, with the power factor of the load, the VA, and the breaker a continuous load would need.
Inputs
Result
Watts to amps chart
Amps for common wattages, power factor 1 (resistive loads like heaters).
| Watts | 12 V DC | 120 V | 240 V |
|---|
How to convert watts to amps
A 1,500 W space heater on 120 V draws 1,500 / 120 = 12.5 A. The same 1,500 W at 240 V is 6.25 A, which is why big loads like ranges, dryers and water heaters run on 240 V. A 10 kW three-phase motor load at 480 V with a power factor of 0.85 draws 10,000 / (1.732 x 480 x 0.85) = 14.2 A.
Power factor
In AC circuits, a heater or a kettle turns all the current into work, so its power factor is 1 and watts = volts x amps. Motors, compressors and many power supplies draw some current that does no work, so the real power in watts is less than volts x amps, the apparent power in VA. The power factor is the ratio, and the lower it is the more amps a load draws for the same watts. Use 1 unless the nameplate gives a power factor or you are working with motors.
Amps and breakers
A breaker is sized for the amps, not the watts. Under the NEC a continuous load, one running for 3 hours or more, may only load a breaker to 80%, which is the same as sizing the breaker at 125% of the load. A 15 A circuit carries 12 A continuous, 1,440 W at 120 V; a 20 A circuit, 16 A or 1,920 W. Wire size follows the breaker; the wire size calculator works it out.
Going the other way? Use the amps to watts calculator, or the kVA calculator for transformers and services.
Questions
How many amps is 1,500 watts?
12.5 amps at 120 volts, 6.25 amps at 240 volts.
How do I convert watts to amps?
Divide watts by volts. For AC, also divide by the power factor; for three-phase, divide by 1.732 as well. 2,400 W at 240 V is 10 A.
How many amps is 1,000 watts?
8.3 amps at 120 V, 4.2 amps at 240 V and 83 amps at 12 V DC.
How many watts can a 15 amp circuit handle?
1,800 W at 120 V, but only 1,440 W for a continuous load running 3 hours or more, which is limited to 80% of the breaker.
How many amps is 100 watts at 12 volts?
8.3 amps. Low-voltage DC loads draw ten times the amps of the same wattage at 120 V, which is why 12 V wiring is heavy.
What is the formula for watts, volts and amps?
Watts = volts x amps (times the power factor for AC). Rearranged: amps = watts / volts and volts = watts / amps.
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