Three-Phase Power Calculator
kW, kVA, kvar and amps for three-phase, single-phase and DC circuits from any one of them at a voltage and power factor, with phase angle and horsepower.
The current a load draws or the power a current carries — real, apparent and reactive — with the √3 and power-factor arithmetic shown, so breaker, cable and transformer figures line up.
Example: 400 V three-phase at 10 A and power factor 0.85: 5.89 kW real, 6.93 kVA apparent, 3.65 kvar reactive, 31.8° lag. A 10 kW load at 400 V and pf 0.9 draws 16.0 A.
√3 for three phases,
cos φ for the part that does work.
Real, apparent and reactive power, where the √3 comes from, and which voltage to enter.
Real, apparent and reactive
Apparent power S = V × I is what the conductors, transformer and breaker must carry. Real power P = S × cos φ is what does work and what the meter bills; the power factor cos φ comes from the load (a motor nameplate, a driver datasheet). Reactive power Q makes up the difference, Q = √(S² − P²), and circulates without doing work. Enter any one of current, kW or kVA and the other two follow at the given voltage and power factor; DC has no power factor.
Three-phase and the √3
A balanced three-phase load carries three times the power of one phase, and the line-to-line voltage is √3 times the phase voltage, so S = 3 × V_phase × I = √3 × V_LL × I. Enter the line-to-line voltage (400, 480, 415 …) as printed on the supply; the page also shows the wye phase voltage. Unbalanced loads, harmonics and delta versus wye connection details are outside the balanced formula.
Motors and nameplates
A motor's rated kW or hp is mechanical output; the electrical input is that figure divided by efficiency, and the current on the nameplate already includes both efficiency and power factor. Enter electrical power here, and prefer the nameplate current where you have it. Horsepower is converted at 745.7 W (mechanical). Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Balanced three-phase power relations P = √3·V_LL·I·cos φ — standard power-systems theory (e.g. Glover, Overbye & Sarma, Power System Analysis and Design, chapter 2)
- NIST Special Publication 811 (2008) — horsepower (electric) 746 W; mechanical horsepower 745.6999 W used here
Last reviewed 19 September 2026. How results are checked: How we verify.