kW to Amps Calculator

Divide the power by the voltage — and by the power factor on AC. Single-phase: amps = watts ÷ (volts × PF). Three-phase: amps = watts ÷ (√3 × volts × PF). DC: amps = watts ÷ volts. So a 3.5 kW (3,500 W) single-phase load at 240 V (230 V) and 0.9 PF draws about 16.2 A.

Power factor is the ratio of real power (kW) to apparent power (kVA) — how “in step” the current is with the voltage. Resistive loads like heaters and kettles are 1.0; motors, transformers and older lighting run 0.7–0.9. If you don’t know, 0.9 is a reasonable general figure, and 0.8 for motor-heavy loads.

The load is spread across three conductors, and the √3 (about 1.73) in the formula reflects that. A 10 kW load at 0.9 PF draws about 46 A single-phase at 240 V but only about 13 A per phase at 480 V three-phase (230/400 V elsewhere) — which is why big loads go on three-phase.

It is the starting point. The figure here is the full-load running current; wires and breakers are then chosen to carry at least that, with allowances for continuous running, grouping and installation method. Use our breaker size and wire size calculators with this current to finish the job.

Motors briefly draw far more than their running current when starting — direct-on-line starts commonly hit 6–8× full-load amps. That surge matters for breaker selection (inverse-time or HACR-rated breakers tolerate it) and generator sizing, but wires are sized on the running current, since the surge lasts under a second.