Three-Phase Power Calculator (kW, kVA, Amps)
Find the current, apparent power (kVA) and real power (kW) of a motor or load from its voltage, power factor and efficiency, or work back from the amps you measured.
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The formulas
- Three phase: kVA = √3 × V × I ÷ 1000; kW = kVA × PF
- Single phase: kVA = V × I ÷ 1000; kW = kVA × PF
Going the other way, I = kVA × 1000 ÷ (√3 × V) for three phase. Efficiency converts electrical input to mechanical output on motors.
Worked example
50 A at 480 V three phase and 0.85 power factor: kVA = 1.732 × 480 × 50 ÷ 1000 = 41.6 kVA, kW = 35.3 kW.
Frequently asked questions
What power factor should I use?
Use the nameplate value if it is there. Lightly loaded induction motors run around 0.7 to 0.85; resistive heaters are 1.0.
Does this give the breaker size?
No. Breaker and wire sizing for motors follow NEC Article 430. Use the wire size calculator for general loads.
Related calculators
This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.