Power Factor Calculator
Enter the real power in watts and the apparent power in volt-amps to find the power factor, the phase angle between voltage and current, and the reactive power. The power factor is the ratio of real to apparent power.
How to use the power factor calculator
- Enter the real (active) power in watts.
- Enter the apparent power in volt-amps.
- Read the power factor, phase angle and reactive power.
Examples
800 W and 1000 VA
realPowerW = 800, apparentPowerVA = 1000
power factor = 0.8, angle = 36.87 deg, reactive = 600 VAR
Unity power factor
realPowerW = 500, apparentPowerVA = 500
power factor = 1, angle = 0 deg, reactive = 0 VAR
Frequently asked questions
What is the power factor formula?
Power factor equals the real power divided by the apparent power, pf = P / S. With 800 W of real power and 1000 VA of apparent power the power factor is 0.8.
How is the phase angle found?
The phase angle is the inverse cosine of the power factor, angle = acos(pf). A power factor of 0.8 corresponds to a phase angle of about 36.87 degrees.
How do I calculate reactive power?
Reactive power is the square root of the apparent power squared minus the real power squared, Q = sqrt(S^2 - P^2). For 1000 VA and 800 W it is 600 VAR.
What is a good power factor?
A power factor near 1 is ideal because almost all the apparent power does useful work. Utilities often want at least 0.9, and low power factors can incur penalties.
Can the power factor be greater than 1?
No. Real power can never exceed apparent power, so the power factor is always between 0 and 1. A value above 1 means the inputs are inconsistent.
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