Three-Phase Power Calculator

Line voltage, V

Current, A

Power factor

Result

Real power, kW5.595
Real power, W5,594.5
Apparent power, VA6,581.8
Reactive, VAr3,467.2
Phase voltage, V219.4
Power per phase, W1,864.8

That root-three factor

Real, apparent and reactive power for a three-phase supply from line voltage, current and power factor.

Three-phase power is line voltage times current times power factor, multiplied by root three. The 1.732 comes from the phases being 120 degrees apart, so they add as vectors rather than arithmetically.

The usual confusion is line against phase voltage. On a 380/220 supply, 380 volts is the line voltage between two phases and 220 the phase voltage to neutral. They too are related by root three, and the three-phase formula takes the line figure.

What this calculator shows

Real power in watts and kilowatts
Apparent and reactive power
Phase voltage and the power carried by a single phase

What to keep in mind

The load is treated as balanced across all three phases. With an unbalanced load each phase has to be calculated separately.
Line voltage — the figure measured between two phases — is what goes into the formula.

FAQs

Where does root three come from?

From the geometry: the phase voltages are 120 degrees apart, and the vector sum of two of them is 1.732 times either one. Hence 380 = 220 × 1.732.

Line voltage or phase voltage?

Line voltage is measured between two phases and is 380 V; phase voltage runs from a phase to neutral at 220 V. Three-phase formulas use the line figure.

Why is three-phase supply better?

For the same power, the current in each conductor is 1.73 times lower, so the cable is smaller. Three-phase motors are also simpler, more reliable and need no starting capacitor.

What is phase imbalance?

Uneven loading, with one phase heavily loaded and another nearly free. It raises the voltage on the light phase, drops it on the heavy one, and puts current in the neutral where a balanced system would have none.

Worked example

A motor on a 380 volt supply

Input: 380 V, 10 A, 0.85 power factor

Output: 5.59 kW real, 6.58 kVA apparent

Note: Phase voltage is 219 volts and each phase carries 1.86 kW. The same motor single-phase would need nearly 26 amps rather than ten.

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Three-Phase Power Calculator

Result

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