Power Factor Calculator

Find the power factor of a circuit by entering the voltage, current, and power below. The calculator also solves the apparent power, reactive power, and estimates the size of capacitor needed to correct it.

watts
amps
volts

Results:

Power Factor:  
Apparent Power:   VA
Reactive Power:   VAR
Correction Cap:   µF


How to Calculate Power Factor

Power factor is a measure of the efficiency of energy use in an electrical circuit, and is represented as a number between 0 and 1. There are a few different types of power used in a circuit, and power factor is the ratio between them.

True power is the actual power used in a circuit. It is represented as P and often measured in watts (W) or kilowatts (kW).

Reactive power is the power that is absorbed or generated by the circuit to maintain voltage. It typically occurs when the current and voltage are not in phase as the result of capacitive or inductive loads. It is represented as Q and measured in volt-amperes reactive (VAR) or kilovolt-amperes reactive (kVAR).

Apparent power is the combination of true power and reactive power. It is represented as S and measured in volt-amperes (VA) or kilovolt-amperes (kVA).

The following formula can be used to solve for power factor:

PF = cos θ = PS

Finding Power Factor for a Single Phase Circuit

To calculate power factor for a single phase circuit we need to know the true power and the apparent power. Use the formulas below to solve for power factor, apparent power, and reactive power.

Power Factor Formula for Single Phase Circuit

PF = P(W)(V(V) × I(A))

Apparent Power Formula for Single Phase Circuit

S(VA) = V(V) × I(A)

Reactive Power Formula for Single Phase Circuit

Q(VAR) = √(|S(VA)|2 – P(W)2)

Finding Power Factor for a Three Phase Circuit

The formula to find power factor on a three phase circuit is a little different, and requires knowing the line to line voltage. These are the formulas to find power factor on a three phase AC circuit.

Power Factor Formula for Three Phase Circuit

PF = P(W)(√3 × V(V) × I(A))

Apparent Power Formula for Three Phase Circuit

S(VA) = √3 × V(V) × I(A)

Reactive Power Formula for Three Phase Circuit

Q(VAR) = √(|S(VA)|2 – P(W)2)

Correcting Power Factor

Because current flow through a circuit is increased as power factor decreases, this can result in wasted energy through inefficiency. Adding capacitance to the circuit can correct for this.

To estimate the amount of capacitance needed to correct, use the formula below.

capacitance(µF) = 1,000,000 × Q(VAR)(2 × π × 60(Hz) × V(V)2)

The calculator also estimates the size of the capacitor needed to correct power factor. It uses this formula and assumes a 60 Hz electrical system.