We all know horsepower is a measurement of how much muscle our hot rods possess. It’s a form of status that dictates our rank among peers and symbolizes how much power we have in our control. But where did the horsepower measurement originate? Linguistically, you might assume that a horse can produce 1 horsepower, but in reality, it's not even close.
In the 18th century, the development of the steam engine provided a reason
to compare the output of horses with that of the engines that could potentially replace them. In 1782, a Scottish engineer named James Watt conducted experiments and found that a 'brewery horse' could produce 32,400 foot-pounds per minute under heavy load. However, that measurement had little to do with the horsepower metric. To arrive at the value of 1 horsepower, Watt averaged the output of 10 horses over the course of a work day. According to Watt’s calculation, it turns out that the maximum output of a horse is around 15 horsepower.
Watt’s motivation for quantifying horsepower was driven by his development of an improved steam engine. To help market his innovation, he used his horsepower calculation to demonstrate how many horses his engine could replace. Buyers were enthusiastic about the idea of replacing horses with machines.