Power Factor Calculator
Calculate power factor (PF), apparent power in kVA, reactive power in kVAR, and the power factor correction capacitor's capacitance in microfarads. Pick single phase or three phase — for three phase, choose line to line or line to neutral voltage — then enter real power, current, voltage, frequency, and the corrected power factor you want. Everything runs locally in your browser.
Select the phase and voltage type
Pick "Single phase" for one AC circuit, or "Three phase" for a balanced three-phase system. For three phase, also choose the voltage type: line to line (between two phases, √3 factor) or line to neutral (phase to neutral, 3× factor).
Enter power, current, voltage, frequency
Type real power P in kilowatts (kW), current I in amps (A), RMS voltage V in volts (default 120) and frequency f in hertz (default 60). All four must be greater than zero, and P must not exceed the apparent power V × I / 1000 — otherwise the power factor would exceed 1.
Set the target PF, press Calculate
Enter the corrected power factor you want (greater than 0, at most 1) and press Calculate. You get power factor, apparent power (kVA), reactive power (kVAR), and the correction capacitor in µF, each shown to at most four decimals. Reset restores the 120 V / 60 Hz defaults.
Power factor calculation formulas
- Single phase power factor formula
- PF = |cos φ| = 1000 × P(kW) / (V(V) × I(A)). For example, a 2.3 kW load drawing 25 A at 120 V has PF = 1000 × 2.3 / (120 × 25) ≈ 0.7667. Apparent power is |S(kVA)| = V(V) × I(A) / 1000, and reactive power is Q(kVAR) = √(|S(kVA)|² − P(kW)²).
- 3 phase power factor formula — line to line voltage
- For balanced three-phase loads measured line to line: PF = 1000 × P(kW) / (√3 × VL-L(V) × I(A)) and |S(kVA)| = √3 × VL-L(V) × I(A) / 1000. For example, 10 kW at 18 A and 400 V line to line gives PF ≈ 0.8019 and S ≈ 12.471 kVA.
- 3 phase power factor formula — line to neutral voltage
- With line to neutral voltage the per-phase power is summed with a 3× factor: PF = 1000 × P(kW) / (3 × VL-N(V) × I(A)) and |S(kVA)| = 3 × VL-N(V) × I(A) / 1000. The two three-phase forms agree whenever VL-L = √3 × VL-N, as balanced wye systems require.
- Power factor correction capacitor calculation
- To correct the power factor to a chosen value: Scorrected(kVA) = P(kW) / PFcorrected, Qcorrected(kVAR) = √(Scorrected² − P²), and the capacitor must supply Qc(kVAR) = Q − Qcorrected. Its capacitance is C(F) = 1000 × Qc(kVAR) / (2πf(Hz) × V(V)²) (for line to neutral, the per-phase value divides by 3 × 2πf × VL-N²); the result is displayed in microfarads. The correction capacitor should be connected in parallel to each phase load.
- Leading or lagging — does it matter?
- The power factor calculation does not distinguish between leading and lagging power factors, and the power factor correction calculation assumes an inductive load. If your corrected target is no better than the current power factor, no capacitor is needed and the capacitance shows 0 µF.
- When does the calculator report an error?
- Voltage, current, frequency and real power must all be greater than zero (each appears in a denominator or fixes the correction target), and the corrected power factor must be greater than 0 and at most 1. Real power above the apparent power V × I / 1000 would mean PF > 1, which is not physical, so it is rejected instead of returning an imaginary reactive power.
Privacy: every calculation runs in your browser tab — no value you type is sent anywhere. This calculator is for educational purposes: results assume balanced sinusoidal RMS values and an inductive load — verify real installations with a meter and a qualified electrician.