How to use Amps to Watts
Enter the current in amps and the voltage, for example 230 V in most of Europe and Asia or 120 V in North America. Set the power factor if you know it, then read the power in watts and kilowatts.
A quick worked example
A 10 amp load on a 230 volt supply draws 10 × 230 = 2,300 watts. On a 120 volt US circuit, a 15 amp breaker allows up to 120 × 15 = 1,800 watts. If a motor has a power factor of 0.8, the 10 amp, 230 volt case drops to 10 × 230 × 0.8 = 1,840 watts of real power.
When the power factor matters
Heaters, kettles and incandescent bulbs have a power factor close to 1, so amps times volts is enough. Motors, compressors and some LED drivers draw current that is out of step with the voltage, so the useful power is lower. The power factor is often printed on the nameplate of the appliance.
The formula
watts = amps × volts × power factor
Examples
- 10 A at 120 V
1,200 W Assumes single-phase AC with the power factor entered (use 1 for DC).
- 16 A at 230 V
3,680 W Assumes single-phase AC with the power factor entered (use 1 for DC).
- 5 A at 240 V, power factor 0.9
1,080 W Assumes single-phase AC with the power factor entered (use 1 for DC).
Limitations and assumptions
Single-phase formula. Three-phase circuits use an extra √3 factor. Always follow electrical codes and a qualified electrician for installations.
Frequently asked questions
What is the formula?
Watts = amps × volts × power factor.
What is the power factor?
The ratio of real power to apparent power, between 0 and 1. Resistive heaters are close to 1.
How do I get kilowatts?
Divide the watts by 1,000.
Does it work for three phase?
No, it assumes single phase or DC.