Power factor calculator
Enter measured real power and apparent power (or volts, amps and watts). The tool shows the power triangle and the kVAR of capacitance needed to reach your target PF.
Capacitor banks on motor circuits can cause over-excitation and resonance with drives and harmonics. NEC Article 460 covers installation. Have a qualified engineer specify correction equipment.
The power triangle
Real power (kW) does the work. Reactive power (kVAR) sloshes back and forth to build magnetic fields in motors and transformers. The wiring has to carry both, and their combination is apparent power (kVA). Drag the angle and watch the hypotenuse, which is what your conductors feel, grow while useful power stays the same.
For 100 kW of work: 115.5 kVA apparent, so 15% more current than at unity power factor.
Correcting power factor
kVAR = kW × (tan(arccos PF₁) − tan(arccos PF₂))Correcting 100 kW from 0.75 to 0.95: tan(arccos 0.75) = 0.882, tan(arccos 0.95) = 0.329, so 100 × 0.553 = 55.3 kVAR of capacitance. Apparent power drops from 133 kVA to 105 kVA, and current falls by the same 21%.
Typical power factors
- Resistive heaters, incandescent lamps: 1.0
- Induction motors at full load: typically 0.8–0.9; much lower when lightly loaded
- Electronics with active PFC (most modern PC and LED drivers above ~75 W): above 0.9
Check the equipment's datasheet; these are general ranges, not design values.
Questions people ask
How do I calculate power factor?
PF = real power (kW) ÷ apparent power (kVA). For a single-phase circuit, PF = W ÷ (V × A).
How much capacitance do I need to correct power factor?
kVAR = kW × (tan(arccos PF1) − tan(arccos PF2)). Correcting 100 kW from 0.75 to 0.95 needs 100 × (0.882 − 0.329) = 55.3 kVAR.
Why does power factor matter?
Low power factor means more current for the same useful power, so bigger conductors and transformers and, on many commercial tariffs, demand or reactive-power charges.