Power Factor Calculator
Calculate power factor, real power, reactive power, and apparent power for AC electrical circuits.
Power factor (PF) measures how efficiently electrical power is used in an AC circuit. A power factor of 1.0 (or 100%) means all power is used productively. Lower values indicate wasted energy.
Key formulas:
Power Factor (PF) = Real Power / Apparent Power = P / S = cos(θ)
Apparent Power: S = V × I (in volt-amperes, VA)
Real Power: P = V × I × PF (in watts, W)
Reactive Power: Q = V × I × sin(θ) (in volt-amperes reactive, VAR)
Relationship: S² = P² + Q² (the power triangle)
What each term means:
- Real Power (P) — the useful power that does actual work (measured in watts, W)
- Reactive Power (Q) — power that oscillates between source and load without doing work (measured in VAR)
- Apparent Power (S) — the total power delivered by the source (measured in VA)
- Phase Angle (θ) — the angular difference between voltage and current waveforms
- Power Factor — cosine of the phase angle, ranges from 0 to 1
Typical power factors:
| Load Type | Power Factor |
|---|---|
| Resistive heater | 1.00 |
| Incandescent bulb | 1.00 |
| LED driver (good) | 0.90–0.99 |
| LED driver (cheap) | 0.50–0.70 |
| Electric motor (loaded) | 0.80–0.90 |
| Electric motor (unloaded) | 0.10–0.30 |
| Fluorescent lighting | 0.50–0.70 |
| Computer power supply | 0.60–0.99 |
| Air conditioner | 0.70–0.90 |
When to use this calculator:
- Sizing electrical panels and wiring
- Calculating utility bills (some charge for low power factor)
- Determining capacitor size for power factor correction
- Electrical engineering coursework
Practical example: A motor draws 10 A at 230 V with a power factor of 0.85. The apparent power is 2,300 VA, but the real power doing useful work is only 1,955 W. The remaining 1,213 VAR is reactive power bouncing back and forth.
Tips:
- Utilities may penalize industrial customers with PF below 0.9.
- Power factor correction capacitors can raise PF and reduce energy bills.
- Leading PF means current leads voltage (capacitive load); lagging means current lags (inductive load).
- Most real-world loads are inductive (motors, transformers) with lagging power factor.