Watts to Amps Calculator
Choose the circuit type, then enter the voltage and either the power or the current. For AC circuits you can include the power factor of the load.
Result
- Real power
- 1,500 W
- Kilowatts
- 1.5 kW
- Apparent power
- 1,500 VA
- Energy used per hour
- 1.5 kWh
Formula
- DC: I = P ÷ V
- AC single-phase: I = P ÷ (V × PF)
- AC three-phase: I = P ÷ (√3 × V × PF), with V measured line to line
- Energy (kWh) = kilowatts × hours
How the Watts to Amps Calculator works
Power is voltage times current. In a DC circuit that is the whole story. In an AC circuit only part of the current does useful work, and that fraction is the power factor. A purely resistive load such as a heater has a power factor of 1. Motors are typically 0.8 to 0.9.
In a balanced three-phase system the power is √3 times the line-to-line voltage times the line current times the power factor. √3 is about 1.732.
Worked example
A 1,500 W heater on a 120 V single-phase circuit draws 1,500 ÷ 120 = 12.5 A. A 10 kW three-phase load at 480 V with a 0.8 power factor draws 10,000 ÷ (1.732 × 480 × 0.8) = 15.04 A.
Frequently asked questions
How many amps is 1,000 watts at 120 volts?
About 8.33 amps for a resistive load, since 1,000 ÷ 120 = 8.33. At 240 volts it is 4.17 amps.
How do I convert kW to amps for three-phase?
Multiply kW by 1,000, then divide by 1.732 times the line voltage times the power factor. At 480 V and unity power factor, 1 kW is about 1.2 amps.
How do I calculate kWh?
Multiply the power in kilowatts by the hours of use. A 1,500 W heater running for 4 hours uses 1.5 × 4 = 6 kWh.
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