Three-Phase Power Calculator

Written byOleh Soloninupdated 25 September 2026

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
WorkingP = √3 × 380 × 10 × 0.85 = 5,594.5 W

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 worked from the line voltage between two phases: P = √3 × V line × I × PF. At 380 V, 10 A and a power factor of 0.85 that is 5,594.5 W.

The phase voltage, between a phase and neutral, is √3 times smaller: 380 ÷ 1.732 = 219.4 V. On a 230/400 V supply at 16 A and a power factor of 1, the power is 11,085 W.

How to use

Enter the line voltage between phases and the current in each phase.
Set the load's power factor: it is on a motor's rating plate, and 1 for a heater.
Read the real, apparent and reactive power, the phase voltage and the power per phase.

Power from the phase current

Each row is a separate run with a balanced load.

All rows come from the calculator on this page.
Voltage	Current	Power factor	Real power	Per phase
380 V	10 A	0.85	5.595 kW	1,864.8 W
380 V	16 A	0.85	8.951 kW	2,983.7 W
380 V	25 A	0.85	13.986 kW	4,662.1 W
380 V	32 A	0.85	17.902 kW	5,967.5 W
380 V	16 A	1	10.531 kW	3,510.3 W
400 V	16 A	1	11.085 kW	3,695 W
400 V	25 A	0.85	14.722 kW	4,907.5 W

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. Reactive power Q = √(S² − P²) assumes sinusoidal voltage and current; with harmonics that root also includes distortion.
Line voltage — the figure measured between two phases — is what goes into the formula.

FAQs

How do I calculate three-phase power?

P = √3 × V line × I × PF, where V line is the voltage between phases. 380 V, 10 A and 0.85 give 5,594.5 W.

How many kW can a 16 A three-phase breaker supply at 380 V?

10.53 kW at a power factor of 1 and 8.95 kW at 0.85, with a balanced load.

Why is there a square root of three in the formula?

In a balanced three-phase system the line voltage is √3 times the phase voltage, so three phases' worth of power, 3 × V phase × I, becomes √3 × V line × I.

What is the difference between line and phase voltage?

Line voltage is between two phases, phase voltage between a phase and neutral. 380 V line is 219.4 V phase; 400 V is 230.9 V.

How do I find a three-phase motor's current from its power?

I = P ÷ (√3 × V × PF), where P is input power: for a motor, the shaft rating divided by the efficiency. For 5.5 kW at the shaft, 0.90 efficiency, 380 V and a power factor of 0.85 that is 10.92 A. The watts and amps calculator has no efficiency field, so enter the input power there — 5,500 ÷ 0.90 = 6,111 W.

What is reactive power on three phases?

The part of apparent power that does no work: Q = √(S² − P²). At 380 V, 10 A and 0.85 it is 3,467.2 VAr.

Worked example

A 380 V motor

Input: 380 V, 10 A, power factor 0.85

Output: 5,594.5 W real and 6,581.8 VA apparent power

Note: Reactive power is 3,467.2 VAr, and each phase carries 1,864.8 W.

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Three-Phase Power Calculator

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