kVA Calculator
Convert between kVA, kW and amps for single and three-phase supplies, for sizing generators and transformers.
About the kVA Calculator
Choose single or three-phase, what you know (amps, kVA or kW), and enter it with the voltage and power factor. The calculator gives the apparent power in kVA, the real power in kW and the current.
kVA is apparent power: volts × amps (× √3 for three-phase). kW is the real power that does work: kVA × power factor. Generators and transformers are rated in kVA because their heating depends on current, whatever the power factor.
The formula
kVA = √3 × V × I ÷ 1000 (3-phase); kW = kVA × PF
Worked example
100 A on a 400 V three-phase supply, power factor 0.8
- kVA = 1.732 × 400 × 100 ÷ 1,000 = 69.28 kVA
- kW = 69.28 × 0.8 = 55.43 kW
Things to keep in mind
- Size generators with a margin (often 20–25%) and allow for motor starting currents.
Questions people ask
Why 0.8 power factor?
It's the standard rating assumption for generators.
What is 400 V?
The usual European three-phase line voltage; the US commonly uses 208 V or 480 V.
What size generator for 50 kW?
50 ÷ 0.8 = 62.5 kVA before any margin.