Power factor is a measure of electrical systems efficiency by an industrial or commercial facility. Use our online AC power factor calculator to find the electrical AC circuit power factor by entering the value of real power(KW) and reactive power (KVAr). Power factor refers to the ratio of total power used to do a work to the apparent power passed in the circuit. The range of power factor would lie between 0 or 1. It is equal to the true power (P) divided by the apparent power.