Power Factor Calculator
Find power factor and power triangle values.
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Formulas
PF = P / S = cos(φ)P = real power (W), S = apparent power (VA), Q = reactive power (VAR). S² = P² + Q².
Power Factor
PF = 1.0: purely resistive (ideal). PF = 0: purely reactive (no useful work). Motors typically 0.7-0.9. Power companies charge penalties for PF below 0.9. Correct with capacitors.
What Power Factor Means
In AC circuits with motors, transformers, or other reactive loads, not all the supplied power does useful work. Power factor is the ratio of real power (that does work) to apparent power (that the supply must deliver):
PF = P / S = cos(φ)P is real power in watts, S is apparent power in volt-amps (VA), and φ is the phase angle between voltage and current.
A power factor of 1.0 is ideal — all delivered power does work. Lower values mean the supply carries extra current that produces no useful output, increasing losses and, for industrial users, electricity charges.
Worked Example
A motor draws 8 kVA apparent power but delivers 6.4 kW of real power:
PF = 6400 / 8000 = 0.8
This 0.8 (lagging) power factor means 20% of the supply capacity is tied up in reactive power doing no work.
Power Factor Reference
| Load type | Typical power factor |
|---|---|
| Incandescent / heater (resistive) | 1.0 |
| Induction motor (loaded) | 0.8 – 0.9 |
| Induction motor (lightly loaded) | 0.2 – 0.5 |
| Fluorescent lighting (uncorrected) | 0.5 – 0.6 |
Frequently Asked Questions
Why does low power factor cost money?
Utilities must supply the full apparent current even though only the real component does work. Many charge industrial customers penalties for power factor below about 0.9.
How do you correct power factor?
Adding capacitors (for inductive loads) supplies the reactive power locally, reducing the current drawn from the supply and raising the power factor toward 1.
What is leading vs lagging?
Inductive loads (motors) make current lag voltage; capacitive loads make it lead. Most industrial loads are lagging, which is why correction usually adds capacitance.