Power Factor Calculator
Power factor from any two of kW, kVA and kVAR, with the phase angle, the line current at your voltage and the capacitor kVAR to reach a target. How it works
Use the Power Factor Calculator
About the Power Factor Calculator
Power factor is real power divided by apparent power: 100 kW drawn as 125 kVA is a power factor of 0.800, with 75.00 kVAR of reactive power and a phase angle of 36.87°. This power factor calculator also sizes the capacitor for a target power factor: 42.13 kVAR takes that 100 kW load from 0.800 to 0.95. It accepts any two of kW, kVA and kVAR, and gives the line current when you type the supply voltage.
Power factor, reactive power and phase angle
| Real power (kW) | Apparent power (kVA) | Power factor | Reactive power (kVAR) | Phase angle |
|---|---|---|---|---|
| 100 | 125 | 0.800 | 75.00 | 36.87° / 0.6435 rad |
| 80 | 100 | 0.800 | 60.00 | 36.87° / 0.6435 rad |
| 95 | 100 | 0.950 | 31.22 | 18.19° / 0.3176 rad |
| 90 | 100 | 0.900 | 43.59 | 25.84° / 0.4510 rad |
| 70 | 100 | 0.700 | 71.41 | 45.57° / 0.7954 rad |
| 50 | 100 | 0.500 | 86.60 | 60.00° / 1.0472 rad |
| 100 | 100 | 1.000 | 0.00 | 0.00° / 0.0000 rad |
| 0 | 100 | 0.000 | 100.00 | 90.00° / 1.5708 rad |
| -40 | 50 | -0.800 | 30.00 | 143.13° / 2.4981 rad |
The page prints reactive power without a unit because it is in the unit of your inputs: kW and kVA give kVAR, W and VA give VAR.
Capacitor kVAR to reach a target power factor
| Real power (kW) | Apparent power (kVA) | Present power factor | Target | Capacitor (kVAR) |
|---|---|---|---|---|
| 100 | 125 | 0.800 | 0.90 | 26.57 |
| 100 | 125 | 0.800 | 0.95 | 42.13 |
| 100 | 125 | 0.800 | 0.98 | 54.69 |
| 100 | 125 | 0.800 | 1 | 75.00 |
| 70 | 100 | 0.700 | 0.90 | 37.51 |
| 70 | 100 | 0.700 | 0.95 | 48.41 |
| 90 | 100 | 0.900 | 0.85 | None needed: already at or above the target |
Qc = kW × (tan θ1 − tan θ2), for an inductive load. The figure is the reactive power to cancel, in the unit of your inputs; a real capacitor bank is chosen from standard ratings for the supply voltage.
Frequently asked questions
- How do you calculate power factor from kW and kVA?
- Divide kW by kVA. 90 kW at 100 kVA is a power factor of 0.900; the reactive power is √(100² − 90²) = 43.59 kVAR and the phase angle acos(0.9) = 25.84°.
- How do I size a capacitor for power factor correction?
- Qc = kW × (tan θ1 − tan θ2), with θ1 = acos(present PF) and θ2 = acos(target PF). For 100 kW at 0.800 corrected to 0.95: 100 × (0.75 − 0.3287) = 42.13 kVAR. Enter the target in the optional field to get this figure.
- Can it tell whether the power factor is leading or lagging?
- No. kW and kVA give the size of the reactive power, not its sign, so the calculator does not report lagging (inductive) or leading (capacitive). The capacitor figure assumes an inductive load, the common case for motors.
- What does a negative power factor mean?
- A negative real power means power flowing back to the source, for example from a generator or solar inverter. -40 kW at 50 kVA gives -0.800 and a phase angle of 143.13°.
- Why does it refuse kW larger than kVA?
- Apparent power is the hypotenuse of the power triangle, kVA² = kW² + kVAR², so real power cannot exceed it. 130 kW with 125 kVA is refused instead of showing a power factor above 1.
- How do I convert between kVA and amps?
- Type the supply voltage and pick the phase, and the page gives the line current from the apparent power: I = kVA × 1,000 ÷ V for single phase, I = kVA × 1,000 ÷ (√3 × V) for three phase with V line to line. 125 kVA at 400 V three phase is 180.42 A; at 230 V single phase it is 543.48 A. The other way, kVA = √3 × volts × amps ÷ 1,000, so 480 V at 120 A three phase is 99.77 kVA; type that in as kVA yourself.
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