Power Factor Correction Calculator
Capacitor kVAR needed to raise power factor from PF1 to PF2, the µF per capacitor for single-phase, delta or star banks, and the drop in line current and losses.
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About this toolWhat is the Power Factor Correction Calculator?
Enter the real power of a plant or machine, its present power factor and the power factor you want, and this calculator gives the capacitor bank size in kVAR. It also converts that into capacitance in microfarads for a single-phase capacitor or for each of the three capacitors in a delta or star (wye) bank at your voltage and frequency.
The results show what the correction buys you: lower line current, less kVA drawn from the transformer and a smaller I²R loss in the cables upstream of the capacitors. A power triangle drawn to scale shows the reactive side shrinking while the real power stays the same.
The multiplier shown with the answer is the same number printed in the "kW multiplier" tables in capacitor catalogues, so you can check the result against a manufacturer chart.
- kVAR from kW and two power factors, with the catalogue multiplier
- Capacitance per capacitor for single-phase, delta and star at 50 or 60 Hz
- Current, kVA and cable loss before and after
- Scaled power triangle
- Warnings for over-correction targets
How to use the Power Factor Correction Calculator
- Enter the real power in kW. Use average demand from a bill or logger rather than a nameplate total.
- Enter the existing power factor and the target. 0.95 is a common target; going past 0.98 rarely pays and risks over-correction at light load.
- Enter the voltage (line to line for three-phase) and frequency.
- Choose single-phase, three-phase delta or three-phase star for the capacitor connection.
- Read the kVAR, the capacitance per capacitor, the current before and after, and the released kVA.
Worked examples
100 kW plant, 0.70 to 0.95, 480 V 60 Hz delta
Input
P = 100 kW, PF 0.70 → 0.95, 480 V, 60 Hz, delta
Output
69.15 kVAR, 265.4 µF per capacitor, current 171.8 A → 126.6 A
The kW multiplier is 0.692, matching catalogue tables. In practice you would buy a 70 or 75 kVAR bank.
250 kW at 400 V 50 Hz, star bank
Input
P = 250 kW, PF 0.78 → 0.95, 400 V, 50 Hz, star
Output
118.4 kVAR, 2,355 µF per capacitor at 230.9 V, current 462.6 A → 379.8 A
Star connection needs three times the capacitance of delta for the same kVAR, but at a lower voltage rating.
Single 2.2 kW motor at 230 V 50 Hz
Input
P = 2.2 kW, PF 0.75 → 0.95, 230 V, 50 Hz, single-phase
Output
1.22 kVAR, 73.2 µF, current 12.75 A → 10.07 A
Capacitors fitted at a motor must not exceed its magnetising kVAR, or self-excitation can occur when it is switched off.
Background and insight
Induction motors, transformers and fluorescent ballasts draw magnetising current that lags the voltage. That reactive current does no work, but it flows through every cable and transformer between the source and the load. Power factor, PF = kW ÷ kVA = cos φ, measures how much of the current is useful. Many utilities add a charge when the monthly PF falls below a threshold, commonly 0.9 or 0.95, or bill on kVA demand.
A capacitor draws leading reactive current that cancels part of the lagging current. With real power P unchanged, the reactive power before correction is P × tan φ1 and after is P × tan φ2, so the capacitor must supply Qc = P × (tan φ1 − tan φ2). Raising 100 kW from PF 0.70 to 0.95 needs 100 × (1.0202 − 0.3287) = 69.15 kVAR. Current falls in proportion to PF1 ÷ PF2, here by 26%, and cable losses (proportional to current squared) fall by about 46%.
Capacitance follows from Q = V² × 2πf × C for each capacitor. A single-phase capacitor across V needs C = Q ÷ (2πfV²). In a three-phase delta bank each of three capacitors sees the full line voltage and supplies Q ÷ 3, so C = Q ÷ (3 × 2πf × V²). In a star bank each sees V ÷ √3, which makes each capacitor three times larger: C = Q ÷ (2πf × V²). Delta banks are therefore usual at low voltage. Standard references include IEEE Std 18 for shunt power capacitors and IEC 60831 for low-voltage self-healing units.
Common use cases
Avoiding utility PF penalties
Size a capacitor bank to keep the monthly power factor above the tariff threshold.
Freeing transformer capacity
See how many kVA correction releases before buying a larger transformer.
Motor capacitor selection
Find the µF for an individual motor capacitor at 50 or 60 Hz.
Teaching the power triangle
Show how kW, kVA and kVAR relate before and after correction.
Tips and limitations
- Correcting to unity is not the goal. Above about 0.98, light-load periods can swing the plant leading, which can raise voltage and upset generators.
- Drives, rectifiers and LED drivers create harmonics. Plain capacitors can resonate with the supply transformer; use detuned (reactor) banks when non-linear load is significant.
- Capacitor kVAR is rated at nameplate voltage. Used at a lower voltage, output falls with the square: a 480 V unit on 440 V gives 84% of its rating.
- Automatic banks switch steps in and out as load changes; a fixed bank suits a steady base load or a single motor.
- Capacitors hold a dangerous charge after switching off; discharge resistors and waiting times are required.
Frequently asked questions
How do you calculate kVAR for power factor correction?
kVAR = kW × (tan(arccos PF1) − tan(arccos PF2)). For 100 kW from 0.70 to 0.95 that is 100 × (1.020 − 0.329) = 69.2 kVAR.
How do I convert kVAR to microfarads?
For one capacitor, C = kVAR × 1000 ÷ (2π × f × V²) farads. For a three-phase delta bank divide by three again, because each of the three capacitors supplies a third. 69.15 kVAR at 480 V 60 Hz in delta is 265 µF per capacitor.
What is a good power factor to aim for?
Most installations target 0.95 lagging. That captures most of the current and loss reduction and stays clear of leading power factor at light load. Check your tariff for the exact threshold.
Why does star connection need more capacitance than delta?
Each star capacitor sees only V ÷ √3, and reactive power scales with voltage squared, so it must be three times larger to give the same kVAR. It can, however, use a lower voltage rating.
Does power factor correction reduce my electricity bill?
It reduces kVA demand charges and power factor penalties where the tariff has them, and trims cable losses slightly. It does not reduce the kWh used by the load itself.
Can I over-correct power factor?
Yes. Too much capacitance makes the power factor leading, raises voltage and can cause self-excitation of motors or instability with generators. Automatic switched banks avoid this when load varies.
Is there an in-depth guide to the Power Factor Correction Calculator?
Yes. “Power Factor Correction: Sizing Capacitors in kVAR and µF” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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