Calculate Power Factor (PF), kVA, kVAR and phase angle (φ) from kW, voltage and current for single-phase and three-phase systems.
A three-phase panel reads 50 kW at 415 V with a measured line current of 87 A:
Enter the same numbers above to see these steps generated automatically.
For the same 10 kW load on 415 V three-phase, the line current rises sharply as PF drops — this is why utilities penalise low PF and why cables, breakers and transformers must be oversized:
| Power Factor | Line Current | vs PF 1.0 |
|---|---|---|
| 1.00 | 13.9 A | — |
| 0.90 | 15.5 A | +11% |
| 0.80 | 17.4 A | +25% |
| 0.70 | 19.9 A | +43% |
| 0.60 | 23.2 A | +67% |
Running at a low PF? Size the capacitor bank in kVAR with our Power Factor Correction Calculator.
| Load Type | Typical PF |
|---|---|
| Resistive heating / incandescent lighting | 1.00 |
| Induction motor (full load) | 0.80 – 0.85 |
| Induction motor (light load) | 0.50 – 0.70 |
| LED drivers (quality) | 0.90 – 0.95 |
| Fluorescent (magnetic ballast, uncorrected) | 0.50 – 0.60 |
| Welding machines | 0.50 – 0.60 |
Measured panel PF matters for feeder sizing — build the full schedule with our Electrical Panel Load Calculator.
Power factor is the ratio of real power (kW) doing useful work to apparent power (kVA) drawn from the supply: PF = kW / kVA = cos φ. A PF of 1.0 means all current does useful work; a low PF means the same kW load draws more current — at PF 0.7 a load draws about 43% more current than at PF 1.0.
PF = kW / kVA, where kVA = V × I / 1000 (single-phase) or √3 × V × I / 1000 (three-phase). kVAR = √(kVA² − kW²), and φ = arccos(PF). Example: 50 kW, 415 V 3-phase, 87 A → kVA 62.54, PF 0.80, kVAR 37.56, φ 36.9°.
In a balanced three-phase system, apparent power is calculated from line-to-line voltage and line current. The √3 (≈1.732) factor comes from the geometry between line and phase quantities: S = √3 × VL-L × Iline.
0.95 or higher is a common design target. Many utilities apply penalty charges when average PF falls below about 0.90 (0.85 in some tariffs). Typical uncorrected values: induction motors 0.80–0.85 at full load, welders 0.5–0.6, resistive heating 1.0.
Lagging — current lags voltage; typical for inductive loads (motors, transformers, reactors). Leading — current leads voltage; caused by capacitive loads or over-compensated capacitor banks. Most industrial plants run lagging and improve PF with capacitor banks sized in kVAR.