A power factor correction calculator for capacitor banks
This power factor calculator works out how much capacitive reactive power — in kVAR — a load needs to move from its present power factor to a target, and what that means in practice: the apparent power and line current before and after, the percentage of current you save, and the capacitance in microfarads for a single-phase capacitor or for each capacitor of a three-phase bank in delta or star.
Use it to size an APFC panel, a fixed motor capacitor or any capacitor bank calculation for power factor correction. You can start from the power factor on a meter, from kW and kVA on an electricity bill, from kW and kVAR, or from measured volts and amps. Defaults suit Indian and European 415 V / 50 Hz supplies; switch to 60 Hz and 480 V or 208 V for North America.
Everything runs in your browser. The results are design estimates for planning and quotations, not a substitute for a site survey, harmonic study or the capacitor manufacturer’s selection data.
How to use the Power Factor Correction Calculator
- Choose Three-phase or Single-phase and enter the real power of the load in kW.
- Under I know the, pick what you have: the present power factor, the kVA, the kVAR, or the measured line current (with the voltage, this gives the power factor).
- Enter the target power factor — 0.95 is a common goal — and the supply voltage and frequency.
- For three-phase banks pick Delta or Star. Optionally add the capacitor’s rated voltage and the size of the bank steps.
- Read the kVAR, the currents and the µF, then use Copy results to paste the working into a report.
Power Factor Correction Calculator features
Four ways to start
Power factor, kVA, kVAR or measured volts and amps — the power triangle fills in the rest.
Capacitance per capacitor
µF for a single-phase unit, or for each of the three capacitors in a delta or star bank.
Nameplate correction
A capacitor delivers its rated kVAR only at its rated voltage; enter that voltage to see which rating to buy.
Step rounding
Round up to standard bank steps and see the power factor you actually end with, including a warning if it goes leading.
Multiplier table
The familiar kVAR-per-kW factors for common present and target power factors, calculated rather than copied.
The formula: kVAR = kW × (tan φ₁ − tan φ₂)
In the power triangle the real power P (kW), reactive power Q (kVAR) and apparent power S (kVA) satisfy S² = P² + Q², and the power factor is cos φ = P ÷ S, so Q = P × tan φ. A capacitor supplies reactive power of the opposite sign, so the kVAR it must provide is the difference between the reactive power now and the reactive power that is allowed at the target: Qc = P (tan φ₁ − tan φ₂).
A capacitor’s reactive power is Q = V² × 2πf × C. On a single-phase supply that gives C = Qc ÷ (2πf V²). In a three-phase delta bank each of the three capacitors sees the line voltage and supplies a third of the total, so C = Qc ÷ (3 × 2πf × V²). In star each capacitor sees V ÷ √3, so it needs three times the delta capacitance for the same kVAR. Because output scales with V², a 440 V capacitor on a 415 V supply gives only (415 ÷ 440)² ≈ 89% of its nameplate kVAR.
Worked example from the US Department of Energy fact sheet Reducing Power Factor Cost (read 24 October 2026): a 100 kW load drawing 100 kVAR has a power factor of 0.71 and an apparent power of 142 kVA. Adding about 67 kVAR of capacitors brings the power factor to 0.95 and the apparent power down to 105 kVA, roughly a 26% cut in current.
Good practice when you size a capacitor bank
- Do not correct to exactly 1.0 with fixed capacitors. When the load falls, the bank over-corrects and the power factor becomes leading, which raises the voltage. Automatic (APFC) panels switch steps in and out to avoid this.
- For a capacitor connected directly across an induction motor, keep its kVAR below the motor’s no-load magnetising kVAR, or the motor can self-excite when switched off.
- Drives, UPSs and other non-linear loads create harmonics that can resonate with capacitors. Use detuned (reactor) banks and get a harmonic assessment where the share of such loads is large.
- Utilities set their own thresholds, incentives and penalties: the DOE sheet notes that many US utilities charge extra below 0.95, while Indian state tariffs set their own limits. Check your tariff order.
Related calculators
Convert between watts, VA and amps with the watt calculator, estimate a building’s demand with the electrical load calculator, choose a transformer with the transformer kVA calculator, and check cable sizes with the wire gauge calculator.
Power Factor Correction Calculator FAQ
How do I calculate the kVAR needed for power factor correction?
Multiply the real power in kW by tan φ₁ − tan φ₂, where φ₁ and φ₂ are the angles whose cosines are the present and target power factors. For 100 kW at 0.70 corrected to 0.95 that is 100 × (1.0202 − 0.3287) = 69.15 kVAR.
How do I convert kVAR to microfarads?
C = kVAR × 1,000 ÷ (2πf × V²) for one capacitor across voltage V. For a three-phase delta bank divide by three more, because the kVAR is shared by three capacitors. 69.15 kVAR at 415 V and 50 Hz in delta is about 426 µF per capacitor.
What is a good power factor?
Most utilities and designers aim for 0.95 or better at the point of supply. Correcting much above 0.98 with fixed capacitors risks a leading power factor at light load.
How does a power factor calculator use kW and kVAR?
The power factor is kW ÷ √(kW² + kVAR²). Pick “Reactive power (kVAR)” in this power factor calculator, enter both values and it works out the present power factor, then the correction to your target.
Why is my capacitor giving less kVAR than its rating?
Capacitor output varies with the square of voltage and in proportion to frequency. A 440 V, 50 Hz rating used on 415 V gives about 89% of its kVAR. Enter the rated voltage in the tool to see the nameplate size to order.
Does power factor correction reduce my electricity bill?
It cuts current, kVA demand and cable losses. Savings depend on your tariff: kVA demand charges and power factor penalties fall, kWh energy barely changes. An estimate, not financial advice.