Three-phase power calculator — kW, kVA, amps
Solve the three-phase power equation P = √3 × V × I × PF — enter voltage and current with power factor to read real power, or voltage and power with power factor to read line current.
Three-phase power equation
Formulas: P (kW) = √3 × V × I × PF / 1000, S (kVA) = √3 × V × I / 1000, Q (kVAR) = √3 × V × I × √(1 − PF²) / 1000
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Frequently asked questions
How do I calculate kW from volts and amps in a three-phase system?
The tool uses P (kW) = √3 × V × I × PF / 1000. At the default 400 V, 20 A and PF 0.85 that gives about 11.8 kW of active power, with apparent power S = √3 × V × I / 1000 at about 13.9 kVA. Reactive power is Q = √3 × V × I × √(1 − PF²) / 1000.
How much current does a three-phase load draw at a given kW?
Line current is solved from I = P × 1000 / (√3 × V × PF). A 15 kW load at 400 V with PF 0.85 needs about 25.5 A. Note that with a purely resistive load (PF = 1) the same power draws about 21.7 A, which is why the power factor matters when sizing conductors and protection.
What is the difference between kW, kVA and kVAR?
kW is the active (real) power that does work, kVA is the apparent power the supply must deliver, and kVAR is the reactive power from magnetizing loads. They are linked by the power factor: kW = kVA × PF, and kVAR = kVA × √(1 − PF²). The calculator returns all three from the same voltage, current and PF inputs.
AO Ctrl provides this tool for reference only.