AC Power Factor Calculator
Calculate power factor, reactive power, and apparent power for AC circuits.
Determines if power factor correction is needed.
Power Factor
In AC circuits, the power factor (PF) measures how efficiently electrical power is being used:
PF = P/S = cos(φ)
Where:
- P = Real power (watts W) — the power actually doing work
- S = Apparent power (volt-amperes VA) — the total power supplied by the source
- φ = Phase angle between voltage and current
- Q = Reactive power (VAR) = √(S² − P²)
Power factor categories:
| Power Factor | Category | Notes |
|---|---|---|
| 1.0 | Unity | Pure resistive load (heaters, incandescent bulbs) |
| 0.95 – 1.0 | Excellent | Well-compensated industrial load |
| 0.80 – 0.95 | Good | Acceptable for most applications |
| < 0.80 | Poor | Utility may charge penalty fees |
| 0.5 or less | Very poor | Significant reactive power problem |
Why power factor matters:
A low power factor means the utility must supply more current than is actually needed for real work. This wastes energy in transmission line losses. That’s why:
- Industrial customers are billed for apparent power (kVA), not just real power (kW)
- Factories with electric motors use capacitor banks to correct low power factor
- Modern variable-frequency drives have near-unity power factor by design
Reactive power Q: Positive Q = inductive load (motors, transformers) — current lags voltage Negative Q = capacitive load (capacitors) — current leads voltage