Three-Phase Power Calculator (kVA, kW, kvar, A, PF)
Three- or single-phase: from voltage, one of amps, kW or kVA, and power factor, get apparent, real and reactive power and current. Power factor from kW and kVA.
Formulas
- Three-phase: S = √3 × V × I, single-phase: S = V × I (V line-to-line for three-phase)
- P = S × cos φ, Q = S × sin φ = √(S² − P²)
- Power factor cos φ = P ÷ S = P ÷ √(P² + Q²)
- I = S ÷ (√3 × V) (three-phase), I = S ÷ V (single-phase)
kVA, kW and kvar
- Real power P (kW) turns into work (heat, rotation); reactive power Q (kvar), such as a motor's magnetization, flows back and forth without doing work; apparent power S (kVA) is their combined size, voltage × current. ABB's Motor guide describes P and Q together making up S, and calls the ratio of kW to kVA the power factor.
- Cables, breakers and transformers are sized by current, so look at kVA (or amps), not kW. The same kW at a lower power factor needs more current: 100 kW at 400 V is 144 A at power factor 1 and 180 A at 0.8.
- To raise the power factor with capacitors, see the power factor correction capacitor calculator.
kVA ↔ current (three-phase, independent of power factor)
| kVA | 220 V | 380 V | 400 V | 440 V |
|---|---|---|---|---|
| 1 | 2.62 | 1.52 | 1.44 | 1.31 |
| 5 | 13.12 | 7.60 | 7.22 | 6.56 |
| 10 | 26.2 | 15.2 | 14.4 | 13.1 |
| 30 | 78.7 | 45.6 | 43.3 | 39.4 |
| 50 | 131.2 | 76.0 | 72.2 | 65.6 |
| 100 | 262.4 | 151.9 | 144.3 | 131.2 |
| 300 | 787.3 | 455.8 | 433.0 | 393.6 |
| 500 | 1312.2 | 759.7 | 721.7 | 656.1 |
| 1000 | 2624.3 | 1519.3 | 1443.4 | 1312.2 |
For motors
A motor nameplate's kW is shaft output; the electrical input is larger by the efficiency. To get current from output kW, use the motor current calculator, which includes efficiency. This calculator converts electrical-side kW, kVA and amps, such as meter readings.
FAQ
How do I convert kVA to kW?
kW = kVA × power factor. At 0.8, 100 kVA is 80 kW. Without the power factor, kVA alone does not give kW.
How many amps is 1 kVA at 380 V three-phase?
1000 ÷ (1.732 × 380) ≈ 1.52 A. The kVA-to-current relation does not involve the power factor.
Can I get the power factor from kW and amps?
With the voltage, yes: power factor = kW × 1000 ÷ (√3 × V × I). Entering kW and kVA (= √3 × V × I ÷ 1000) under «Find the power factor» gives the same.
What is 2.2 kVA at 220 V single-phase?
2200 ÷ 220 = 10 A (set the supply to single-phase).
To get current from motor output (kW, HP) and efficiency, use the Motor Current Calculator. To raise the power factor with capacitors, use the Power Factor Correction Capacitor Calculator. For a power meter's CT ratio, secondary current and burden, use the CT Ratio & Burden Calculator. For heater kW and heater current, use the Heater Power Calculator.