Power Factor Calculator
kW, kVA and kVAR, plus capacitor size to correct power factor.
About this tool
Enter real power in kW and the current power factor to get kVA, kVAR and the phase angle. Add a target power factor, the supply voltage and frequency to size correction capacitors.
The power triangle and correction
AC loads draw real power (kW) that does work and reactive power (kVAR) that sloshes back and forth in magnetic and electric fields. Together they make apparent power (kVA), and power factor = kW Ć· kVA. Induction motors, transformers and older lighting typically run at 0.7ā0.85, which means more current, larger cables and, for many businesses, reactive-power charges. Capacitors supply reactive power locally: the correction needed is kVAR = kW Ć (tan Ļā ā tan Ļā). Raising a 50 kW load from 0.75 to 0.95 needs about 27.7 kVAR and cuts the supply current by about 21%. Capacitance is C = kVAR Ć· (2ĻfVĀ²) for single-phase; for a delta-connected three-phase bank each capacitor is a third of that at line voltage, about 183 ĀµF per phase for this example at 400 V and 50 Hz. Honest limits: over-correction gives a leading power factor, harmonics from variable-speed drives can make capacitors resonate, and switched banks need proper protection. Have correction specified by an electrical engineer. The watts to amps calculator and the electricity cost calculator are related.
Frequently asked questions
What is a good power factor?
0.95 or higher. Many utilities penalise power factors below about 0.9.
How do I calculate kVAR?
kVAR = ā(kVAĀ² ā kWĀ²), or kW Ć tan(arccos PF).
How much capacitance do I need to correct power factor?
First find kVAR = kW Ć (tan Ļ1 ā tan Ļ2), then C = kVAR Ć 1000 Ć· (2Ļ f VĀ²) in farads for single-phase.
Why does low power factor matter?
It increases current for the same useful power, causing more losses, larger cables and possible utility charges.
Is my data sent anywhere?
No. Everything is calculated in your browser, and nothing is stored or sent.