Calculate horsepower from force, distance, and time measurements, or convert between different power units including mechanical HP, metric HP, watts, and more.
Horsepower is a unit of power that measures the rate at which work is done. Originally developed by James Watt in the late 18th century to compare steam engine output to horse power, it has become the standard measurement for engine power across various applications.
Understanding different horsepower measurements and conversions is essential for comparing engine performance, electrical motor specifications, and mechanical power requirements across different systems and industries.
Where: Force = applied force, Distance = distance moved, Time = time duration
Where: Work = Force × Distance (measured in joules or foot-pounds)
| Type | Symbol | Watts | Definition | Common Use |
|---|---|---|---|---|
| Mechanical Horsepower | hp(I) | 745.7 | 550 ft⋅lbf/s | US automotive industry |
| Metric Horsepower | PS/CV | 735.5 | 75 kgf⋅m/s | European automotive |
| Electrical Horsepower | hp(E) | 746.0 | Exactly 746 W | Electric motors |
| Boiler Horsepower | bhp | 9809.5 | 34.5 lb water/hour evaporated | Steam boilers |
| Hydraulic Horsepower | whp | 745.7 | Fluid power systems | Hydraulic pumps |
Watt to Horsepower: 1 Mechanical HP = 745.7 watts
Kilowatt to Horsepower: 1 kW = 1.341 Mechanical HP
BTU/hour to Horsepower: 1 HP = 2544.4 BTU/hour
Foot-pounds/second to Horsepower: 1 HP = 550 ft⋅lbf/s
Horsepower measures how quickly work can be done and determines top speed and high-RPM performance. It's calculated as: HP = (Torque × RPM) ÷ 5,252
Torque measures rotational force and determines acceleration and pulling power at low speeds. It's most important for towing and initial acceleration.
Automotive: Engine horsepower ratings help compare vehicle performance, but consider torque curves, weight, and gearing for real-world performance.
Industrial: Motor horsepower ratings determine capability for driving pumps, compressors, conveyor systems, and manufacturing equipment.
Marine: Boat engine horsepower affects speed and acceleration, but hull design and weight significantly impact actual performance.
Aviation: Aircraft engine power-to-weight ratio is critical for performance, with power measured at various altitudes and conditions.
| Measurement Type | Description | Typical Values | Applications |
|---|---|---|---|
| Brake Horsepower (BHP) | Power at engine crankshaft | 10-15% higher than WHP | Engine specifications |
| Wheel Horsepower (WHP) | Power delivered to wheels | Actual usable power | Vehicle performance |
| Indicated Horsepower (IHP) | Power calculated from cylinder pressure | Theoretical maximum | Engine development |
| Shaft Horsepower (SHP) | Power transmitted through shaft | Marine and aircraft engines | Propeller applications |
Drivetrain Loss: Automatic transmissions typically lose 18-25% of engine power, while manual transmissions lose 12-18%.
Parasitic Loss: Engine accessories (alternator, power steering, AC) can consume 10-20 horsepower depending on load.
Heat Loss: Internal combustion engines convert only 25-35% of fuel energy to mechanical work, with the rest lost as heat.