Power Factor Calculator
Enter the real power and apparent power of an AC load to find its power factor, the reactive power and the phase angle between voltage and current.
Result
- Power factor as a percentage
- 80%
- Phase angle
- 36.87°
Formula
- Power factor = real power (kW) ÷ apparent power (kVA)
- Reactive power (kVAR) = √(kVA² − kW²)
- Phase angle = arccos(power factor)
How the Power Factor Calculator works
Real power does the work and is measured in kilowatts. Apparent power is voltage times current and is measured in kilovolt-amperes. Their ratio is the power factor. The difference is reactive power, which flows back and forth to magnetise motors and transformers.
The three form a right triangle. A low power factor means more current for the same useful power, which raises losses and can bring utility penalties.
Worked example
A load drawing 80 kW and 100 kVA has a power factor of 80 ÷ 100 = 0.8. The reactive power is √(100² − 80²) = 60 kVAR and the phase angle is 36.87°.
Frequently asked questions
What is a good power factor?
Utilities generally want 0.9 or higher, and many charge extra below 0.85 to 0.95. A purely resistive load is 1.0.
How do I convert kVA to kW?
Multiply kVA by the power factor. A 100 kVA load at 0.8 power factor uses 80 kW.
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