Power – current converter: kW, kVA, A, HP
Enter one quantity (output power, horsepower, kVA or current) and see the others instantly, single- or three-phase, with power factor and efficiency.
Formulas used
S = k · U · I k = 1 single-phase, √3 three-phase P_el = S · cos φ active power drawn P_out = P_el · η output (shaft) power 1 CP = 735.5 W 1 HP = 745.7 W
- U = nominal voltage: 230 V single-phase (line–neutral), 400 V three-phase (line–line)
- cos φ = power factor; 1 for resistive loads (heaters, incandescent lamps)
- η = efficiency; 1 for resistive loads, 0.85–0.95 for motors
Worked example
A three-phase 11 kW motor (output power), cos φ = 0.85, η = 0.9, at 400 V:
P_el = 11 / 0.9 = 12.22 kW S = 12.22 / 0.85 = 14.38 kVA I = 14,380 / (√3 · 400) = 20.75 A 11 kW / 0.7355 = 14.96 CP
Typical three-phase motor currents at 400 V
Calculated with cos φ = 0.85 and η = 0.9 for every size. Small motors are weaker on both, so their real current is higher; use the nameplate data.
| Output (kW) | CP | kVA | Current (A) |
|---|---|---|---|
| 0.37 | 0.5 | 0.5 | 0.7 |
| 0.75 | 1.0 | 1.0 | 1.4 |
| 1.5 | 2.0 | 2.0 | 2.8 |
| 2.2 | 3.0 | 2.9 | 4.2 |
| 3.0 | 4.1 | 3.9 | 5.7 |
| 4.0 | 5.4 | 5.2 | 7.5 |
| 5.5 | 7.5 | 7.2 | 10.4 |
| 7.5 | 10.2 | 9.8 | 14.2 |
| 11.0 | 15.0 | 14.4 | 20.8 |
| 15.0 | 20.4 | 19.6 | 28.3 |
| 22.0 | 29.9 | 28.8 | 41.5 |
| 30.0 | 40.8 | 39.2 | 56.6 |
| 37.0 | 50.3 | 48.4 | 69.8 |
Frequently asked questions
What is the difference between kW and kVA?
kW is real (active) power, the part that becomes mechanical work or heat. kVA is apparent power, voltage times current. Their ratio is the power factor: kW = kVA × cos φ. Cables, fuses and transformers are sized on kVA (current), not kW.
What power factor and efficiency should I use for a motor?
For three-phase induction motors of a few kW, typical values are a power factor of 0.8–0.88 and an efficiency of 85–93%. The exact figures are on the motor nameplate; small motors are lower, so their real current is higher than the table shows.
How do I convert kW to amps for three-phase?
I = P / (√3 × U × cos φ × η), with U the line-to-line voltage (400 V). An 11 kW motor with cos φ 0.85 and η 0.9 draws about 20.8 A.
What is the difference between metric horsepower and HP?
Metric horsepower (CP, PS) is 735.5 W; mechanical horsepower (HP, used in the US) is 745.7 W, about 1.4% more. European nameplates normally show kW.
Does the calculator include starting current?
No. The result is the current at rated operation. Direct-on-line motors draw 5–8 times rated current briefly at start-up, which matters when choosing protection.