Calculate the efficiency of an AC electrical system by comparing real power to apparent power.
Last updated: March 2026 | By ForgeCalc Engineering
In electrical engineering, the power factor (PF) of an AC electrical power system is defined as the ratio of the real power flowing to the load, to the apparent powerin the circuit. It is a dimensionless number in the closed interval from -1 to 1.
A power factor of less than one means that the voltage and current are not in phase, reducing the instantaneous product of the two. Real power is the capacity of the electricity for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit.
Measured in Watts (W). The actual power consumed by the load to perform work.
Measured in Volt-Amperes Reactive (VAR). Power that oscillates between source and load.
Measured in Volt-Amperes (VA). The total power delivered to the circuit.
A low power factor means higher current is needed to deliver the same amount of real power. This leads to higher energy losses in the distribution system and may result in penalties from utility companies.
Inductive loads like motors, transformers, and fluorescent lighting ballasts are the most common causes of low (lagging) power factor.
Power factor can be improved by adding capacitors (for inductive loads) or inductors (for capacitive loads) to the circuit. This is called power factor correction.
A power factor of 1.0 is called unity. It means the voltage and current are perfectly in phase, and all delivered power is real power.
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