Power Factor Correction Calculator (Capacitor kVAr)
By Santaji GadepatilinUpdated October 27, 2026
Inductive loads such as motors draw reactive current that loads up cables and transformers without doing useful work. Adding capacitors supplies that reactive power locally, raising power factor and cutting your kVA demand. Learn how to calculate capacitor bank kVAr and the basics of capacitor bank sizing for power factor correction.
How to use the power factor correction calculator
Enter the active load in kW, the present and target power factor, and the supply voltage and frequency. You get the capacitor kVAr required, the capacitance per phase for a delta-connected bank, the kVA before and after, and how much the line current falls.
For more background, read Power Factor Improvement Calculation and Power Factor, kW, kVA and kVAr Explained.
Power factor correction formula
Qc = P × (tan φ₁ − tan φ₂), φ = cos⁻¹(PF)
For a delta-connected three-phase bank, each capacitor sees the line voltage:
C per phase = Qc ÷ (3 × 2πf × VL²)
Example
100 kW at 0.75 PF, corrected to 0.95 at 415 V, 50 Hz:
- tan φ₁ = 0.882, tan φ₂ = 0.329
- Qc = 100 × (0.882 − 0.329) = 55.3 kVAr
- kVA falls from 133.3 to 105.3 and line current falls by 21%
kVAr multiplier table (kVAr per kW)
| Present PF | to 0.90 | to 0.95 | to 0.98 | to 1.00 |
|---|---|---|---|---|
| 0.60 | 0.849 | 1.005 | 1.130 | 1.333 |
| 0.65 | 0.685 | 0.840 | 0.966 | 1.169 |
| 0.70 | 0.536 | 0.692 | 0.817 | 1.020 |
| 0.75 | 0.398 | 0.553 | 0.679 | 0.882 |
| 0.80 | 0.266 | 0.421 | 0.547 | 0.750 |
| 0.85 | 0.135 | 0.291 | 0.417 | 0.620 |
| 0.90 | 0.000 | 0.156 | 0.281 | 0.484 |
Multiply the factor by the load kW to get the kVAr required.
Why correct power factor?
- Lower bills: avoid utility penalties for low PF and reduce kVA maximum demand charges.
- Free up capacity: the same transformer and cables can carry more kW.
- Lower losses: I²R losses in cables and transformers fall with current.
- Better voltage: less reactive current means less voltage drop.
Fixed vs automatic correction
- Fixed capacitors at individual motors suit constant loads. Size them to about 90% of the motor’s no-load magnetising kVAr to avoid self-excitation.
- APFC panels (automatic power factor correction) switch capacitor steps as the plant load changes. They are the usual choice for a main LV board.
Harmonics
Capacitors lower the system’s resonant frequency. With VFDs, UPSs and other non-linear loads, check harmonic levels with the THD calculator and use detuned reactors where needed.
Frequently asked questions
How do I calculate the kVAr needed for power factor correction?
kVAr = kW × (tan φ₁ − tan φ₂), where φ₁ = acos(present PF) and φ₂ = acos(target PF). For 100 kW from 0.75 to 0.95 you need about 55.3 kVAr.
What power factor should I aim for?
Most utilities penalise below 0.90–0.95. A target of 0.95–0.98 is common. Avoid correcting to unity or leading, which can cause over-voltage and resonance.
Why does the current fall after correction?
The capacitor supplies the reactive current locally, so the supply only carries the active part plus less reactive current. Current falls in proportion to PF₁ ÷ PF₂.
Do I need detuned capacitors?
Where drives and other non-linear loads create harmonics, use detuned (reactor-protected) banks — typically 7% detuning — to avoid harmonic resonance.