Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. The term was coined by Scottish engineer James Watt in the late 18th century to compare the output of steam engines with the power of draft horses. There are many different standards and types of horsepower, but two common definitions used today are the mechanical horsepower (or imperial horsepower), which is about 745.7 watts, and the metric horsepower, which is approximately 735.5 watts.
Horsepower is calculated by multiplying the amount of force (in pounds) by the speed (in feet per second) . For example, if an engine can generate 200 pounds of force and move at a speed of 2 feet per second, the engine horsepower would be 400 (200 x 2) .
Although most countries now use the SI unit watt for measurement of power, horsepower is still commonly used to express the rate at which mechanical energy is expended, especially in the automotive industry.
