Power factor is the ratio of true power or watts to apparent power or volt amps.
They are identical only when current and voltage are in phase than the power factor is 1.0. The power in an ac circuit is very seldom equal to the direct product of the volts and amperes. In order to find the power of a single phase ac circuit the product of volts and amperes must be multiplied by the power factor. Ampmeters and voltmeters indicate the effective value of amps and volts. True power or watts can be measured with a wattmeter.