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About this tool
Convert three-phase voltage, current and power factor into kW, kVA and output power.
Three-Phase Power Calculator turns line-to-line voltage, line current, power factor and efficiency into apparent power, real power, reactive power and shaft output, using the balanced three-phase relationships S = √3 × V × I, P = S × pf and Q = √(S² − P²). It is aimed at electricians, panel builders and plant engineers sizing a feeder or checking a nameplate. At the default 400 V, 50 A, pf 0.9 and 95% efficiency it returns 34.64 kVA apparent, 31.18 kW input and about 29.62 kW output.
Open Three-Phase Power Calculator on AltFTool — it loads instantly in your browser.
Enter "Line-to-line voltage (V)", "Line current (A)", "Power factor" and "Efficiency (%)", or click the "400 V · 50 A" example preset.
Watch the Result panel recompute live: kW input plus rows for apparent power (kVA), reactive power (kVAr) and estimated output (kW).
Use the Copy button for the summary or Download to save it as three-phase-power-calculator.txt.
Apparent, real and reactive power are all derived from the same voltage and current, so you can see the power triangle instead of converting between units by hand.
Power factor gives electrical input power and efficiency then gives mechanical output, which keeps the two figures people most often conflate on a motor nameplate distinct.
The voltage field is explicitly line-to-line and the current is line current, removing the √3 mistake that comes from mixing phase and line quantities.
Apparent power S = √3 × V_line-to-line × I_line, and real power P = S × power factor. So 400 V at 50 A gives √3 × 400 × 50 = 34,641 VA, or 34.64 kVA, and at a power factor of 0.9 that is 31.18 kW.
kVA is apparent power, the total the supply must carry; kW is real power, the part that does work. They are related by power factor: kW = kVA × pf, so at pf 0.9 a 100 kVA supply delivers 90 kW, and the shortfall shows up as reactive power in kVAr.
Use the nameplate value if there is one. Failing that, induction motors under load typically sit around 0.85 to 0.90, resistive loads such as heaters are close to 1.0, and lightly loaded motors can drop below 0.7 — assume low rather than high, because underestimating pf sizes conductors and generators conservatively.
No. The maths assumes a balanced sinusoidal three-phase system, so it does not model phase imbalance, harmonic distortion from VFDs and rectifiers, inrush, or duty cycle. Treat the result as an estimate and have a qualified electrical engineer confirm cable sizing, protection and compliance with the standards that apply where you are.
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