Electrical reference tools · No account

Watts Calculator

Calculate real electrical input power in watts and kilowatts, plus apparent power in VA, from voltage, current and AC power factor.

Formula and units

DC: P = V × I. Single phase: P = V × I × PF. Balanced three phase: P = √3 × V × I × PF. S = P / PF for AC.

How to use these results

For AC use RMS readings. For balanced three phase, enter line-to-line voltage and line current. Real power W and apparent power VA differ unless PF = 1. This is electrical input power; motor mechanical output needs efficiency data.

Verify critical electrical work with a qualified professional and applicable manufacturer instructions.

Worked example

120 V × 10 A × PF 0.8 = 960 W and 1,200 VA. Balanced 400 V three-phase at 10 A and PF 0.8 = 5,542.563 W.

Reference

Formula background: Schneider Electric — Definition of reactive power. The assumptions and input validation above define this calculator’s scope.