Power Factor Calculator
Calculate power factor (PF = P/S), real power (W), reactive power (VAR), apparent power (VA), phase angle, and power factor correction capacitor size.
Known Quantities
Power Factor Correction (optional)
Typical Power Factors by Load Type
| Load Type | Typical PF | Type |
|---|---|---|
| Resistive heater / incandescent lamp | 1.0 | Unity |
| LED lamp (with driver) | 0.8–0.95 | Lagging |
| Fluorescent lamp (with ballast) | 0.5–0.9 | Lagging |
| Induction motor (full load) | 0.8–0.9 | Lagging |
| Induction motor (no load) | 0.1–0.3 | Lagging |
| Large transformer | 0.8–0.9 | Lagging |
| Capacitor bank | ~0 | Leading |
Frequently Asked Questions
Power factor (PF) is the ratio of real power (W) to apparent power (VA): PF = P ÷ S = cos(φ), where φ is the phase angle between voltage and current. PF ranges from 0 to 1. A PF of 1.0 (unity) means all power is used as real work; a lower PF means more reactive power and wasted grid capacity.
Real power P (watts) does actual work — runs motors, heats resistors. Reactive power Q (VAR) stores and releases energy in inductors/capacitors — it does no useful work but must be supplied. Apparent power S (VA) is the vector sum: S = √(P² + Q²). The power triangle relates all three: S² = P² + Q².
For inductive loads (motors, transformers), power factor is improved by adding capacitors in parallel, which supply reactive power locally. The required capacitance: C = Q_correction ÷ (2πf × V²), where Q_correction = P × (tan φ₁ − tan φ₂). Many utilities charge penalties for PF below 0.9 or 0.95.
Lagging power factor: current lags voltage, caused by inductive loads (motors, transformers). Leading power factor: current leads voltage, caused by capacitive loads. Unity power factor (PF = 1): purely resistive load, current and voltage are in phase. Most industrial loads are lagging.
Power Triangle Formulas
S² = P² + Q² (apparent power is hypotenuse of the power triangle)
PF = P/S = cos(φ) | tan(φ) = Q/P | sin(φ) = Q/S
Power factor correction capacitor: Q_c = P × (tan φ₁ − tan φ₂), then C = Q_c / (2πf × V²)
- P in watts (W): energy doing real work per second
- Q in volt-amperes reactive (VAR): reactive energy oscillating back and forth
- S in volt-amperes (VA): total apparent load on the supply
- Phase angle φ = arccos(PF): current-voltage phase displacement