Size a power-factor correction capacitor bank: Qc = P(tan φ1 − tan φ2).
Enter the load and the existing & target power factors to get the kVAr required, plus the apparent-power and line-current savings.
For design guidance only. Always verify with a qualified engineer.
About this power factor correction calculator
This free power factor correction calculator sizes the shunt capacitor bank needed to raise an installation's power factor from its existing value to a target. It is built for electrical designers, M&E contractors and facilities engineers who want to cut reactive-power (kVAr) charges, free up transformer and cable capacity, and reduce line current. Enter the active load in kW, the existing and target power factors, and the supply arrangement. The calculator returns the capacitor rating in kVAr plus the apparent-power and current savings. Everything runs in your browser; nothing is uploaded.
How power factor correction is calculated
The maths comes straight from the power triangle. For a constant active power P, each power factor gives a phase angle φ = arccos(pf) and a reactive power Q = P·tan φ. The capacitor rating is the difference between the existing and target reactive powers: Qc = P(tan φ1 − tan φ2), the standard relation given in IEEE 1036 (Guide for Application of Shunt Power Capacitors) and the Schneider Electric Electrical Installation Guide to IEC 60364. Apparent power is S = P/pf per IEEE 1459, so correction lowers S and frees capacity. Line current follows I = P/(V·pf) for single-phase or I = P/(√3·V·pf) for three-phase; because P is fixed, the current falls in proportion to 1/pf, giving a reduction of (1 − pf1/pf2)×100 %.
Frequently asked questions
What power factor should I target?
A target of 0.95 is a common practical aim. It removes most of the reactive demand and any utility kVAr penalty without the cost and resonance risk of chasing unity. Correcting much beyond 0.98 gives diminishing returns and can risk over-correction at light load.
Does the supply voltage change the kVAr result?
No. The capacitor rating Qc depends only on the active power and the two power factors. The voltage and phase selection only convert apparent power into line current, so they affect the current figures but never the kVAr you need.
Why is my capacitor value negative?
A negative or zero result means the target power factor is at or below the existing one, so no correction is required. Set a target power factor above the existing value to size a real capacitor bank.