Power Factor Calculator
The power factor from real and apparent power or the phase angle, the reactive power, and the capacitor size in kVAR and µF that corrects it to a target, for single-phase or three-phase.
Result…
How it's calculated
PF = P ÷ S = cos φ S = P ÷ PF · Q = P × tan φ = √(S² − P²) Capacitor: Qc = P × (tan φ1 − tan φ2) C = Qc ÷ (2πf V²) single-phase or star (per phase, V line-to-line) · C = Qc ÷ (3 × 2πf V²) delta (per phase)
Power factor is the share of the current that does useful work. Real power P (kW) runs the load; reactive power Q (kVAR) flows back and forth to build the magnetic fields of motors and transformers; apparent power S (kVA) is what the cables and supply must carry, with S² = P² + Q². PF = P ÷ S, which is also the cosine of the phase angle between voltage and current. A low power factor means more current, bigger cables and, on many tariffs, extra charges. Capacitors supply reactive power locally: to go from φ1 to a target φ2 you need Qc = P × (tan φ1 − tan φ2) kVAR. The capacitance follows from Q = V²ωC, split across three capacitors on a three-phase supply.
Your numbers, step by step
About the Power Factor calculator
This power factor calculator finds how well a load uses the current it draws, and what capacitor would improve it. Start from the real power in kW with the apparent power in kVA, the phase angle, or a power factor you already know. It returns the power factor, the apparent and reactive power and the phase angle. Enter a target power factor, the supply voltage and frequency, and whether the supply is single-phase or three-phase with a delta or star capacitor bank. It then sizes the correction capacitor in kVAR with Qc = P × (tan φ1 − tan φ2), gives the capacitance in µF, and shows how much the apparent power, and so the current, falls. It suits facility managers reading a utility bill, electricians planning correction and students learning the power triangle.
How to use it
- Choose what you know under “I know”, then enter “Real power P” and the second value: “Apparent power S”, “Phase angle φ” or “Power factor now”.
- Enter the “Target power factor”, or leave it blank if you only want the power factor and reactive power.
- Pick the “Supply”; for three-phase, choose whether the “Capacitor bank connected in” delta or star.
- Enter the “Voltage” (line-to-line for three-phase) and the “Supply frequency”.
- Read the capacitor kVAR and µF, then pick the nearest standard capacitor rated for your voltage.
Worked example
A three-phase load uses 45 kW and draws 60 kVA. Its power factor is 45 ÷ 60 = 0.75, a phase angle of 41.41°, and the reactive power is √(60² − 45²) = 39.69 kVAR. To reach 0.95, tan φ falls from 0.8819 to 0.3287, so the capacitor is 45 × (0.8819 − 0.3287) = 24.90 kVAR. A delta bank on 400 V, 50 Hz needs 165.09 µF per phase. The apparent power drops to 45 ÷ 0.95 = 47.37 kVA, about 21% less current.
Updated
Questions people ask
How do I calculate power factor?
Divide the real power in kW by the apparent power in kVA. If you know the phase angle between voltage and current instead, the power factor is the cosine of that angle.
How do I size a capacitor for power factor correction?
Use Qc = P × (tan φ1 − tan φ2), where φ1 is the angle now and φ2 the angle at the target. For the capacitance, C = Qc ÷ (2πf × V²), divided by 3 again for each capacitor of a delta bank on a three-phase supply.
What is a good power factor?
1 is the ideal, where all the current does useful work. The level a supplier expects, and whether it charges for a lower one, depends on the country, the supplier and the tariff, so check your own contract.
What is the difference between kW, kVA and kVAR?
kW is the real power that does work, kVAR is the reactive power that builds magnetic fields in motors, and kVA is what the supply must carry. They form a right triangle: kVA² = kW² + kVAR². The three-phase power calculator gets them from volts and amps.
Can I correct too far?
Yes. Adding more capacitance than needed makes the load leading, which can raise the voltage when the load is light. Aim for the target rather than for exactly 1, and switch capacitor steps with the load where it varies.
When is this calculation not enough?
It assumes clean sine waves and a lagging load. Drives, inverters and other electronics create harmonics that can overload plain capacitors. Have a qualified electrician or power engineer survey the site before installing correction.