The History Of Horsepower

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The term horsepower is actually one of the oldest marketing tricks. We all know the term, and it’s become synonymous with the idea “more is better.” Is that true, though? Here we’ll dive into the history of where this unit of measurement actually comes from, and the reason horsepower was created in the first place.

What Is Horsepower

First, let’s get into what horsepower is. Horsepower (hp) is a unit of power and is now most often associated with measuring the output of engines or motors. The higher the number, the more powerful the engine (you gotta Hemi in that, bro?). 

There are two common distinct standards for measurement (of course there can’t just be a singular unit), mechanical/imperial horsepower and metric horsepower. Horsepower even has its own fancy formula, but we’ll get into that in a minute.

A James Watt Invention

So why horsepower and not “cowpower” or “dogs-playing-tug-o-war-power?” We have Scottish inventor James Watt to thank for creating this term. In 1763 Watt was tasked with repairing a steam engine, and instead of fixing the problem, he created an entirely upgraded version of the engine.

Steam engines were built to replace the work and labor of animals. Caring for oxen or horses (which were some of the most common labor animals) requires a lot of time and money and is a never-ending task. Building a mechanical device for pushing and pulling tasks is more efficient, has less strength limitations, and doesn’t require regular feedings or clean up (at least not in the traditional sense). 

So with Watt’s new and improved engine, he needed to convince people to buy it. How could he convince people his engine was superior to that trash his competition was selling? Simple, create a completely new unit of measurement that only his engine had.

Creating A New Scientific Formula

Watt needed a term for power that was appealing, but also easy for people to understand. Watt recalled a passage from The Miner’s Friend, where author and engineer Thomas Savery compared the work and output of a steam engine to that of horses. He said how an engine might be made to do the work of five, ten, or even fifteen horses. This gave Watt an idea.

Watt studied the work capabilities of farm horses and ponies and unscientifically determined a horse could move 32,572 (which he rounded up to 33,000) foot-pound force per minute (ft⋅lbf/min). Watt’s calculations were based on how quickly a horse could turn a mill-wheel (144 times an hour), and just went from there.

written out scientific equation for figuring out horsepower
Horsepower scientific formula

The mill-wheel turns were converted to the distance the horse technically traveled during that period of time, plus Watt’s estimate of the weight a horse could pull (180 pounds-force), and just like that an entirely new unit of measurement was born. 


Watt’s measurements are not truly accurate, but he now had a way to set his engines apart from the others. He claimed his engine was powerful enough to do the work of ten horses—or that it had ten horsepower. 

People were receptive and the usage of the term took off. Horsepower started being used by other companies, solidifying it in the lexicon, and is still used as a unit of measurement today. 

Watt’s contribution to the engineering world got him his own dedicated unit of measurement—yes, that kind of watt is named after James Watt.

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