Free Engineering Tool
Power and motors
Three-Phase Power and Current Calculator
Know the kW and want the amps, or measured the amps and want the kW. Works for three-phase and single-phase, with power factor and motor efficiency.
- Free
- No sign-up
- Runs in your browser
- Your numbers never leave your device
Inputs
Supply
I know the
kW
V
%
Readout
I-A
Real power
-kW
Apparent power
-kVA
Reactive power
-kVAR
Line current
-A
Shaft output
-kW
Phase angle
-°
Formulas
3-phase: P = √3 × V × I × PF · 1-phase: P = V × I × PF
kVA = P / PF · kVAR = √(kVA² − kW²)
For a motor rated by its shaft output, the electrical input is the shaft kW divided by efficiency. A 30 kW motor at 92% efficiency draws about 32.6 kW from the supply.
Use it to check a reading
- Clamp one phase with a clamp meter and compare the amps with what this tool predicts for the nameplate kW. A big gap means the motor is lightly loaded, or something is wrong.
- Unequal phase currents point to supply imbalance or a winding problem. See how to check three-phase imbalance.
Limits
The result is the full-load figure for the values you enter. Starting current, harmonics and a non-sinusoidal waveform are not covered, and the real power factor of a motor falls sharply at light load.
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