The ratio of the actual power in watts developed by an a.c. system, as measured by a wattmeter, to the apparent power indicated by voltmeter and ammeter readings and usually measured in volt-amperes (VA) rather than watts. If the voltage and current are sinusoidal the power factor, P/VI, is equal to the cosine of the phase angle between them. The power factor is also equal to the ratio of the resistance, R, to the impedance, Z, and thus indicates the dissipation in an insulator, inductor, or capacitor.