Converting amperes to kilowatts turns a breaker or clamp meter reading into the real power a load draws. The amp to kw formula changes slightly between single phase and three phase, so this guide covers both.

The amp to kw formula (single phase)

For DC and single phase AC at unity power factor:

kW = (V × A) ÷ 1000

V is the voltage and A is the current. So 16 A at 400 V is (400 × 16) ÷ 1000 = 6.4 kW. The amps to kw calculator does the multiply and the divide by 1000 for you.

The amp to kw 3 phase formula

Three phase adds the square root of three and the power factor:

kW = 1.732 × V × A × PF ÷ 1000

V is the line voltage. The square root of three appears because the three windings share the load. On a 400 V three phase feeder at 16 A and a power factor of 0.9, kW = 1.732 × 400 × 16 × 0.9 ÷ 1000, about 9.98 kW. If your supply is rated in kVA rather than amps, the kVA to kW conversion guide applies the same power factor step.

Why power factor matters

Motors and other reactive loads pull current that does no real work, so leaving the power factor at 1.0 overstates the kW. Read it from the nameplate or find it with the power factor calculator.

To go the other way, from power back to current, use the kW to amps calculator.

Common mistakes

• Using current alone. You need the voltage as well; current does not set power by itself.
• Skipping power factor. On motors the real kW is below volts times amps divided by 1000.
• Forgetting the square root of three. A three phase load needs the 1.732 factor.

Quick reference

Single phase: kW = V × A ÷ 1000. Three phase: kW = 1.732 × V × A × PF ÷ 1000. Every online calculator on CalculateGuide is free, so you can check both cases in seconds.