Power Factor Calculator
Calculate apparent and reactive power, and the capacitor kVAR needed to correct a power factor.
About the Power Factor Calculator
Enter the real power, current power factor, target power factor, supply voltage and frequency, single or three-phase. The calculator gives the capacitor kVAR and capacitance needed, and the drop in current and apparent power.
Power factor is real power ÷ apparent power. Motors and transformers draw reactive power that does no work but still loads cables and transformers, and many utilities charge for low power factor (often below 0.9 or 0.95). Capacitors supply that reactive power locally. Have a qualified electrician size and install correction equipment.
The formula
S = P ÷ PF; Q = √(S² − P²); Qc = P (tan φ₁ − tan φ₂); C = Qc ÷ (2πfV²)
Worked example
A 10 kW single-phase load at PF 0.75, corrected to 0.95 on 240 V, 60 Hz
- Apparent power: 10 ÷ 0.75 = 13.33 kVA
- Correction: 5.53 kVAR (about 255 µF)
- Current falls from 55.6 A to 43.9 A
Questions people ask
Why not correct to 1.0?
Over-correction risks a leading power factor and resonance; 0.95–0.98 is typical.
What uses reactive power?
Induction motors, transformers, fluorescent ballasts.