Power Factor Correction Calculator
Estimate the capacitor bank size required to improve a load from its current power factor to a target power factor.
Introduction
The power factor correction calculator estimates the capacitor bank size needed to improve an electrical load from its current power factor to a target power factor. This is a common calculation for industrial plants, commercial buildings, workshops, and distribution systems with inductive loads such as motors, pumps, compressors, welders, and HVAC equipment. Poor power factor increases current demand and can reduce the effective capacity of cables, transformers, and switchgear.
Improving power factor can reduce line current, reduce losses, improve voltage regulation, and help avoid utility penalties where reactive demand is billed. This page gives a quick planning result in kVAr so engineers can estimate the size of capacitor bank required before making a final equipment selection.
This is especially useful for motor-heavy systems where a quick capacitor sizing estimate can support energy, loading, and power-quality decisions.
Formula
Qc = P x (tan(phi1) - tan(phi2))
Where phi1 = arccos(current power factor) and phi2 = arccos(target power factor).
Variable Definitions
Qc = capacitor bank size in kVAr
P = active power in kW
phi1 = phase angle at the current power factor
phi2 = phase angle at the target power factor
Units
Active power is entered in kilowatts, and power factor is entered as a decimal value between 0 and 1. The result is displayed in kVAr because that is the standard rating used for power factor correction capacitors and automatic capacitor banks.
Worked Example 1
A 75 kW load operates at 0.76 power factor and needs to be improved to 0.95.
phi1 = arccos(0.76)
phi2 = arccos(0.95)
Qc = 75 x (tan(phi1) - tan(phi2))
The required capacitor bank is about 36.46 kVAr.
The final selected size is usually matched to the nearest standard capacitor bank step.
Worked Example 2
For a 30 kW load operating at 0.80 power factor with a target of 0.95:
Qc = 30 x (tan(arccos(0.80)) - tan(arccos(0.95)))
The required correction is about 13.47 kVAr.
This gives a practical starting point for bank selection.
Practical Notes
Capacitor banks should not be oversized because overcorrection can create a leading power factor and new system problems. Harmonic content, switching steps, load variation, and resonance risk should also be considered. Use this calculator for planning, then confirm the capacitor arrangement and protection details in the final design.