Watts to amps and amps to watts
Calculate current from power or power from current: choose the voltage (12–400 V), circuit (1 or 3 phase) and cos φ — the calculator applies Ohm's law for AC circuits.
Conversion formulas
- Single phase: I = P/(U·cosφ), P = I·U·cosφ
- Three phase: I = P/(√3·U·cosφ), P = √3·I·U·cosφ
- Apparent power: S = √3·U·I (kVA), active: P = S·cosφ (kW)
Typical values
| Power | 230 V 1-ph | 400 V 3-ph |
|---|---|---|
| 2 kW | 8.7 A | 2.9 A |
| 3.5 kW | 15.2 A | 5.1 A |
| 7 kW | 30.4 A | 10.1 A |
| 10 kW | 43.5 A | 14.4 A |
| 15 kW | — | 21.7 A |
| 30 kW | — | 43.3 A |
How to use
Choose “power → current” to size a breaker and cable, or “current → power” to estimate a load. For motors and transformers enter cos φ (0.7–0.9); for heaters and lamps use 1.0.
Related calculators
- Breaker selection by power — breaker-selector
- Cable size by current — cable-calculator
- Voltage drop — voltage-drop
FAQ
How many amps in 1 kW at 230 V?
With cos φ = 1: 1000/230 ≈ 4.3 A. In a 400 V three-phase network: 1000/692 ≈ 1.4 A per phase.
How to convert amps to kilowatts?
P = I·U·cosφ/1000 (1-phase) or P = √3·I·U·cosφ/1000 (3-phase). For 16 A at 230 V: 16×230 ≈ 3.7 kW.
Why is the current lower in a 3-phase network?
The current is distributed over three phases: I = P/(√3·U). At 400 V the factor √3×400 ≈ 692 — the current is about 3× lower than single-phase for the same power.
What is cos φ?
The power factor: the ratio of active to apparent power. ≈ 1 for heaters and lamps, 0.7–0.9 for motors, 0.5–0.9 for fluorescent lamps.