How the calculation works
Single-phase: kVA = V·I/1000; three-phase: kVA = 1.732·V·I/1000 (V = line-to-line). kW = kVA·PF, kVAR = √(kVA² − kW²).
Worked example
3Φ, 480 V, 50 A, PF 0.85: 41.57 kVA, 35.3 kW, 21.9 kVAR.
Common mistakes to avoid
- Using line-to-neutral voltage in the three-phase formula; use line-to-line voltage.
- Confusing kW with kVA when sizing a generator or transformer.
- Assuming a power factor of 1.0 for motor loads.
Frequently asked questions
Which voltage for 3Φ?
Line-to-line (e.g. 208, 480).
Why is the three-phase factor 1.732?
It is √3, which comes from the 120° phase shift between line-to-line voltages in a balanced three-phase system.
What is a typical motor power factor?
Lightly loaded induction motors can run between roughly 0.3 and 0.6; fully loaded motors are usually 0.8 to 0.9. Use nameplate data when you have it.
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