Convert power in kilowatts or horsepower to current in amps, or amps to kilowatts and kVA, for DC, single-phase and three-phase supplies. Enter the voltage, power factor and, for a motor rated by its shaft output, the efficiency.
Worked example
These are example values. Change any entry above and press Calculate to run your own numbers.
Power entered
15 kW (20.115 hp)
Current
25.471 A
Apparent power
17.647 kVA volts x amps (x √3 for three-phase)
This is the calculated current for the operating point you entered. It is not a motor full-load current rating. For motor branch circuits, overloads and protective devices, use the nameplate and the tables in your electrical code.
How it works
The current a load draws depends on its power, the supply voltage, the type of supply and, on AC, the power factor. Three-phase supplies carry the same power at lower current than single-phase, which is why larger equipment is three-phase.
The formulas
DC: I = P ÷ V
Single-phase AC: I = P ÷ (V × PF)
Three-phase AC: I = P ÷ (√3 × V × PF) (V is line-to-line)
Electrical input power = shaft output power ÷ efficiency
Apparent power: kVA = √3 × V × I ÷ 1,000 (three-phase) or V × I ÷ 1,000 (single-phase)
Reference tables
Amps per kW, three-phase, at common voltages
Line voltage (V)
Amps per kW
208
2.776
230
2.51
240
2.406
380
1.519
400
1.443
415
1.391
460
1.255
480
1.203
575
1.004
600
0.9623
690
0.8367
At a power factor of 1 and 100% efficiency. Divide by the real power factor and efficiency for an actual motor, or use the calculator above.
Frequently asked questions
How do you convert kW to amps for a three-phase load?
Divide the power in watts by √3 (1.732) times the line voltage times the power factor. A 15 kW load on 400 V three-phase at a power factor of 0.85 draws 15,000 ÷ (1.732 × 400 × 0.85) = 25.5 A.
How do you convert kW to amps for single-phase or DC?
For single-phase, divide the watts by the voltage times the power factor: 2.3 kW at 230 V and a power factor of 1 is 10 A. For DC there is no power factor, so 1 kW at 24 V is 41.7 A.
What power factor should I use?
Use 1 for resistive loads such as heaters. For induction motors the power factor depends on the motor and its load and is usually well below 1, often around 0.8 to 0.9 near full load. The motor nameplate or datasheet gives the real value, and it is lower at light load.
Why does efficiency matter for a motor?
A motor's hp or kW rating is its shaft output. It draws more electrical power than that, by its losses. Entering the efficiency raises the input power, and the current, to what the supply actually delivers. A 10 hp motor at 90% efficiency draws about 8.3 kW.
Can I size conductors or breakers from this result?
Not on its own. This is the calculated current at the operating point you entered. For motor circuits, electrical codes specify the full-load current to use from tables, plus separate rules for conductors, overload and short-circuit protection, so use the nameplate and the code. Our contactor cross-reference tool covers motor sizing against published NEMA and IEC tables.
