Power factor

(electricity) The ratio of the average (or active) power to the apparent power (root-mean-square voltage times rms current) of an alternating-current circuit. Abbreviated pf. Also known as phase factor.

The ratio of watts average power (the average power measured in watts) to the apparent power of an alternating-current circuit. By definition, the equation below holds, which is the ratio of instrument readings.

A watt-meter indicates average power, and electrodynamometer or iron-vane instruments show rms voltage and current. For the steady-state ac circuit under sinusoidal voltage and current, pf = cos θ, where θ is the phase angle between the voltage and current. This definition is restricted to sine waves of the same frequency.

In an alternating current, the ratio of the average power (expressed in watts) to the apparent power (expressed in volt-amperes).