Three-Phase Power Calculator

Why three-phase power needs its own formula

Three-phase power delivers electricity across three conductors, each carrying current offset by 120 degrees from the others. This staggered arrangement is what makes three-phase motors run smoothly and lets three-phase systems deliver more power per amount of conductor material than single-phase systems.

Worked example

For a 400V line voltage system drawing 20A per line at 0.9 power factor:

P = √3 x V(line) x I(line) x PF = 1.732 x 400 x 20 x 0.9 = 12.47 kW

Frequently asked questions

Why the square root of 3? It comes from the vector sum of three currents 120 degrees apart in a balanced system - the math works out so that combined three-phase power is exactly √3 (about 1.732) times what a naive single-phase calculation using line voltage and current would suggest.

What kind of equipment uses this? Industrial motors, large HVAC compressors, and commercial building electrical services are almost always three-phase, since three-phase motors are smaller, more efficient, and vibrate less than single-phase motors of the same power rating.