After searching through the archive under the tag horsepower, horsepower history, history horsepower and horsepower history I didn't see this question asked but where and why do we use "horse" in the term horsepower when an engine's power is mechanical? Was the term horsepower created to come engine performance versus the power of a horse?
The origin of the word horsepower comes literally from the horse and buggy days. 1 horse pulling a load of 330 lbs of coal or whatever 100 feet above ground in 1 minute generated 1 horsepower.
1 Hp= 330lbs X 100 Ft / 1 minute
33,000 foot-pounds per minute.
With the advent of electrical power the equivalent power was stated in watts or kilowatts.
1 Hp= 745.7 watts or .7457 Kw.