kVA Calculator

kW is real power — the work actually done. kVA is apparent power — the volts × amps the supply must deliver, which is larger whenever current and voltage are out of step. They are linked by the power factor: kW = kVA × PF. Transformers, generators and supplies are rated in kVA because their windings carry the full apparent current regardless of how much of it does useful work.

Single-phase: amps = kVA × 1,000 ÷ volts. Three-phase: amps = kVA × 1,000 ÷ (√3 × volts). So a 100 kVA three-phase transformer at 480 V supplies about 120 A per phase (144 A at 400 V), and a 5 kVA single-phase generator at 240 V gives about 20.8 A (21.7 A at 230 V).

Multiply by the power factor: kW = kVA × PF. A 100 kVA supply at 0.8 PF delivers up to 80 kW of real power. Going the other way, kVA = kW ÷ PF — an 80 kW load at 0.8 PF needs the full 100 kVA of supply capacity.

The part of the apparent power that shuttles back and forth without doing work — it magnetises motors and transformers. It follows from the power triangle: kVAr = √(kVA² − kW²). Utilities charge large customers for it, which is why power factor correction pays: raising PF shrinks the kVAr and frees up supply capacity.

Use the measured or nameplate figure when you have it. Otherwise: 0.8 is the standard assumption for mixed and motor loads (and how generators are rated), 0.9–0.95 suits modern commercial buildings with corrected loads, and 1.0 applies only to purely resistive loads like heaters.