Power Factor Calculator

Power factor equals real power divided by apparent power, pf = P / S. It is the cosine of the phase angle between voltage and current. With 800 W of real power and 1000 VA of apparent power the power factor is 0.8.

The phase angle is the inverse cosine of the power factor, angle = acos(pf), reported in degrees. A power factor of 0.8 gives 36.8699 degrees, while a power factor of 1 gives 0 degrees.

Reactive power is the vertical leg of the power triangle, Q = sqrt(S^2 - P^2), measured in volt-amps reactive (VAR). For 1000 VA of apparent power and 800 W of real power it comes out to exactly 600 VAR.

Watts (W) measure real power that does work, volt-amps (VA) measure apparent power the source must supply, and volt-amps reactive (VAR) measure power that sloshes back and forth in inductors and capacitors. The three form a right triangle with S as the hypotenuse.

A power factor near 1 is ideal because nearly all the apparent power does useful work. Many utilities expect at least 0.9 for larger customers, and lower values can trigger penalty charges or require larger conductors.

No. Real power can never exceed apparent power, so the ratio stays between 0 and 1. If you enter a real power larger than the apparent power, the tool refuses the result instead of returning a value above 1.

No. This calculator returns the magnitude of the power factor and the angle, not its sign. Inductive loads such as motors lag while capacitive loads lead, but that direction is not encoded in the plain P and S values you enter here.

Yes, as long as you enter the total three phase real power in watts and the total three phase apparent power in volt-amps. The ratio is the same whether you feed it single phase or balanced three phase totals.

No. The math runs entirely in your browser using the same engine that powers the tests, so your power values never leave your device and nothing is logged.