What inventor first used the term "Horse Power"?

James Watt first used the term “horsepower” to compare the output of steam engines with the work performed by horses.

In the late 18th century, Watt was improving steam engines that replaced horses and other machines in mines and factories. Customers needed an understandable way to compare an engine’s productive capacity with the familiar power of a draft horse, so Watt developed horsepower as a marketing and measurement concept.

Watt estimated that one horse could perform 33,000 foot-pounds of work per minute. That figure became the traditional imperial horsepower, although real horses can produce different amounts of power depending on the task and duration. The unit is therefore a historical estimate, not a universal biological measurement.

Horsepower later became widely used for engines, turbines, and electric motors. It is also distinct from the watt, the SI unit of power, which was named after James Watt himself.