Power Factor Correction Calculator
Enter load kW, current PF and target PF to get the capacitor bank size in kVAR, the kVA capacity you free up and how much line current drops.
Open calculatorLast updated: 2026-09-15
How the calculation works
- The tool converts both power factors to phase angles and takes the difference of their tangents.
- That tangent difference times the real power gives the reactive kVAR the capacitor bank must supply.
- It then shows the kVA before and after — the freed capacity in transformers and cables — and the line current reduction.
Worked example
Interpreting the result
Correcting PF does not reduce the energy the load consumes; it reduces the reactive current the supply must carry. Benefits appear as lower demand charges, less voltage drop, freed transformer capacity and lower I²R losses. Most utilities penalize below 0.90–0.95; correcting beyond ~0.95 yields little and risks overvoltage at light load.
Assumptions
- Steady, linear load — motors and transformers, not harmonic-rich drives.
- Correction applied at the load or distribution board, not the utility meter.
Limitations
- Loads with variable PF need an automatic capacitor bank with a PF controller, not one fixed bank.
- Harmonic-rich environments (VFDs, rectifiers) require detuned/filtered capacitors to avoid resonance.
- Do not size capacitors for a motor larger than recommended by NEC 460 — overcorrection can cause self-excitation.
Correct only to 0.95 — past that you pay to overcorrect
The kVAR needed to move PF from 0.75 to 0.95 is substantial; moving from 0.95 to 1.00 needs far less in absolute terms, yet that last step is where capacitors become dangerous rather than useful. At light load an oversized fixed bank drives the PF capacitive and the voltage above nominal — a condition that stresses motors and trips variable-speed drives. That is why professional practice targets 0.95, uses automatic banks for variable loads, and never sizes motor capacitors beyond the NEC 460 recommendation: a capacitor fixed to a motor that overcorrects can self-excite the motor after disconnection, with damaging voltage spikes.
Frequently asked questions
What is a good power factor?
0.95 is a common target: most utility penalties start below 0.90–0.92, and gains above 0.95 are small compared with the capacitor cost.
Does correcting power factor save energy?
It saves a little — the I²R losses in your cables drop with the current — but the main financial benefit is avoiding reactive demand charges and freeing installed capacity.