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How this is calculated#

The tool converts between current, apparent power, real power and reactive power. It works on one phase or on three. It does not read a standard. The method is the power triangle.

1. Inputs. You pick one phase or three. You enter the voltage, the current and the power factor. On three phases the voltage is the line voltage.
2. Apparent power. On three phases, S = √3 × V × I ÷ 1000. On one phase, S = V × I ÷ 1000. The result is in kVA.
3. Real power. P = S × power factor. The result is in kW.
4. Reactive power. Q = √(S² − P²). The result is in kvar.

Enter the line voltage on three phases, such as 400 V. Enter the phase voltage on one phase, such as 230 V.

Worked example#

• 50 A at 400 V on three phases, power factor 0.9. The apparent power is 34.64 kVA. The real power is 31.18 kW. The reactive power is 15.1 kvar.

Limits#

The tool assumes a balanced load. It assumes a sine wave. A load with harmonics needs a true RMS reading. The tool does not size a cable or a device. Use the cable size calculator for that. A motor has efficiency as well as power factor. Use the motor tool for its full load current.

Use the tool to check a meter reading, a motor plate or a supply request. For a load in kW, the full load current tool works the other way. A low power factor raises the kVA for the same kW. The power factor correction tool finds the capacitor size.

See also: kVA to amps at 400 V, Current and power factor to kW and Power factor and reactive power.