Horsepower vs. Kilowatts: Mechanical HP, Metric HP, and Converting Engine Power
October 21, 2026
Power measures how fast energy is delivered. The SI unit is the watt, with 1,000 watts in a kilowatt. Engines and motors are often rated in horsepower, a unit that goes back to James Watt, who wanted to compare steam engines to the work of draft horses. There are several horsepower definitions, which differ by less than 1.5%, but the difference still shows up in published specifications.
The mechanical (imperial) horsepower used in the United States and UK is 745.7 watts. The metric horsepower (PS or CV, from the German Pferdestärke and French cheval-vapeur) is 735.5 watts. The electrical horsepower used for motors is exactly 746 watts. To convert, 100 kW = 134.1 mechanical hp = 136.0 metric hp.
Skip the math and get your answer instantly:
Open the Speed Calculator →Conversion Factors
Kilowatts to mechanical horsepower: multiply by 1.34102. Mechanical horsepower to kilowatts: multiply by 0.7457. Kilowatts to metric horsepower: multiply by 1.35962. Metric to mechanical horsepower: multiply by 0.98632. So a 150 PS engine is 110.3 kW, which is 147.9 mechanical hp.
When comparing car specifications across countries, check which unit is used. A European car rated at 150 PS and an American one at 150 hp differ by about 1.4%, which is small but not zero.
| kW | Mechanical hp | Metric hp (PS) |
|---|---|---|
| 50 | 67.1 | 68.0 |
| 75 | 100.6 | 102.0 |
| 100 | 134.1 | 136.0 |
| 150 | 201.2 | 203.9 |
| 300 | 402.3 | 407.9 |
Real-World Examples
A compact car with a 1.5-liter engine rated at 110 kW produces 147.5 mechanical hp. An electric vehicle motor listed at 200 kW is 268 hp. A 1.5 hp pool pump motor draws about 1.1 kW of mechanical output, but because motors are 80% to 90% efficient, its electrical input is closer to 1.3 kW. A 5 hp air compressor motor delivers 3.73 kW. A human can sustain about 0.1 hp (75 watts) over a day, and an elite cyclist can produce 400 watts, over half a horsepower, for a few minutes.
Peak power is not sustained power. Engines are rated at specific rpm; the power at other speeds is lower.
Power, Torque, and Speed
Power is torque times rotational speed. In SI units, power (W) = torque (N·m) × angular speed (rad/s). In customary units, horsepower = torque (lb·ft) × rpm ÷ 5,252. An engine producing 300 lb·ft of torque at 5,252 rpm makes exactly 300 hp, which explains why torque and horsepower curves cross at that speed on a dyno chart. At 3,000 rpm, 300 lb·ft gives 171 hp.
Torque gets you moving, but power determines how quickly you can do work, including how fast the vehicle can accelerate at higher speeds.
Power Needed to Move a Vehicle
At steady speed, the power required to overcome air drag and rolling resistance rises quickly with speed because drag grows with the cube of speed in terms of power. A typical car needs roughly 15 to 20 kW (20 to 27 hp) at 60 mph on level ground, around 25 to 30 kW at 75 mph, and much more at higher speeds. Doubling the speed needs about eight times the power to overcome drag, which explains the fuel economy loss at highway speeds.
Related Units
BTU per hour (1 hp = 2,545 BTU/h), tons of refrigeration (1 ton = 3.517 kW), and boiler horsepower (9.81 kW) are also used. For appliances, wattage is the common rating: a 1,500 watt space heater is about 2 hp of heat output, but unlike motors, it converts all its input to heat.
Frequently Asked Questions
How many watts are in a horsepower?
745.7 watts for mechanical horsepower, 735.5 for metric.
How do I convert kW to hp?
Multiply kilowatts by 1.341 for mechanical horsepower.
What is PS?
Pferdestärke, the German metric horsepower, equal to 735.5 watts.
How are horsepower and torque related?
Horsepower = torque in lb·ft × rpm ÷ 5,252.
Why does power needed rise so quickly with speed?
Aerodynamic drag power grows with the cube of speed.