kW, hp and PS: why horsepower conversions differ
Compare mechanical hp and metric PS, use a two-way conversion table and understand what to check on a motor nameplate.
One name, different definitions
Mechanical horsepower (hp) and metric horsepower (PS) have different definitions. Here hp means mechanical horsepower, not electrical or boiler horsepower. If an HP label is ambiguous, confirm its definition with the manufacturer.
Constants and direction
1 hp is approximately 0.745699872 kW; 1 PS equals 0.73549875 kW. Divide kW by the relevant constant to obtain horsepower; multiply horsepower by the constant to obtain kW. Round the displayed answer, not each intermediate step.
| kW | hp | PS |
|---|---|---|
| 0.75 | 1.0058 | 1.0197 |
| 1.5 | 2.0115 | 2.0394 |
| 2.2 | 2.9502 | 2.9912 |
| 3.7 | 4.9618 | 5.0306 |
| 5.5 | 7.3756 | 7.4779 |
| 7.5 | 10.0577 | 10.1972 |
Compare 5 hp and 5 PS
5 hp is about 3.7285 kW; 5 PS is about 3.6775 kW, a difference of about 0.0510 kW. The same number does not represent equal shaft power. Conversely, 2.2 kW is approximately 2.9502 hp or 2.9912 PS.
Conversion is not a motor replacement decision
A nameplate may show 2.2 kW and 3 HP due to rounding or product labeling conventions. Replacement also depends on rated speed, torque, voltage, frequency, current, duty and mounting dimensions. Shaft-power conversion does not determine electrical consumption or electricity cost.
Connect the conversion to torque
Convert 5 hp to 3.7285 kW and use T = 60000 × P ÷ (2π × n) at 1500 RPM to obtain about 23.7364 N·m. For 5 PS at the same speed, the result is about 23.4117 N·m. These are mathematical operating-point relationships, not starting-torque or motor-range guarantees.