Why convert kW to amps
Machinery, heaters, HVAC compressors, and EV chargers list their draw in kilowatts. The circuit that feeds them is defined by amps — the breaker rating, the wire gauge, the disconnect size. This conversion is the step between a nameplate and a panel schedule: it tells you the current a kW-rated load will pull so you can check it against an existing circuit or design a new one.
Three things shape the answer. Voltage sets the baseline — the same kW at 240 V draws half the current it would at 120 V. The system type matters — a three-phase feed spreads the load across three conductors, cutting the per-line current by about 42%. And for motors and electronic loads, the power factor pushes the current up, because some of it is reactive and does no work.
The kW to amps formula
Single-phase:
Three-phase, line-to-line voltage:
Worked example
The calculator’s defaults are 2.4 kW on a single-phase 240 V circuit at a power factor of 0.8.
Convert to watts:
Divide by voltage and power factor:
The load draws 12.5 A. If it were a resistive 2.4 kW heater instead — power factor 1 — the same circuit would carry only 10 A. The 2.5 A difference is the reactive current that a power factor of 0.8 implies.
kW to amps reference (single-phase, PF 1)
| Power | 120 V | 240 V |
|---|---|---|
| 1 kW | 8.3 A | 4.2 A |
| 2 kW | 16.7 A | 8.3 A |
| 3 kW | 25 A | 12.5 A |
| 5 kW | 41.7 A | 20.8 A |
| 7.5 kW | 62.5 A | 31.3 A |
| 10 kW | 83.3 A | 41.7 A |
For a motor load, divide each figure by the power factor. For three-phase, divide by 1.732 as well.
From running current to circuit size
The current here is the steady operating draw. The breaker and conductor go above it:
- Continuous loads (on 3+ hours) are sized to 125% of the current, so a 12.5 A continuous load wants a circuit rated at least 15.6 A — a 20 A breaker in practice.
- Motor inrush briefly reaches several times the running current; the breaker must ride through it without tripping.
- Derating for high ambient temperature or bundled conductors can force the wire up a gauge.
Common mistakes
- Wrong system type. Selecting single-phase for a three-phase load overstates the current by ~73%.
- Power factor 0.8 for a resistive heater. Use 1.0, or the current reads 25% high.
- Sizing the breaker to the raw current instead of applying the 125% continuous margin.
For the reverse, use the amps to kilowatts calculator. To convert to apparent power for generator sizing, see kW to kVA.