How this calculator works
Average real power is the apparent power multiplied by power factor. For a balanced three-phase load, the total is three times the power in one phase. Line-to-line voltage is sqrt(3) times phase voltage in a wye supply, which gives the familiar sqrt(3) multiplier with line current. This model assumes balanced sinusoidal operation; use measured total power factor when distortion matters.
Formula
P = k V I PF, where k = 1 for single phase, sqrt(3) for three-phase line-to-line voltage, or 3 for three-phase line-to-neutral voltage.
Worked example
At 120 V RMS, 10 A and power factor 0.8, real power is 960 W. A balanced three-phase load at 230 V line-to-neutral, 2 A and unity power factor uses 1380 W.
Advertisement
Frequently asked questions
Do I enter peak voltage?
Use RMS values. A sinusoidal peak voltage divided by sqrt(2) gives its RMS value.
Can the power factor be zero?
Yes when finding real power: it produces zero average watts. It cannot recover an unknown voltage or current.
Why are there two three-phase options?
Line-to-line and line-to-neutral measurements differ by sqrt(3) in a balanced wye system. Choose the reference used by your meter.