Why is ‘horse’ used to measure engine power?

Even in the mid-1700s marketing played a big part in a start-up's success.

Meryl D'Souza October 3, 2016

We here at EDGAR certainly like our cars, as you may have noticed with our regular reviews - the most recent of which is a Porsche 911 Turbo.

Whatever they may start with, when petrolheads compare their motors inevitably the debate comes down to horsepower. It's a strange term of measurement though, isn't it? Typically, units of physical quantities are named after scientists who discover them, not a four-legged animal.

The story behind horsepower

In the 1750s, Scottish inventor James Watt was working on steam engines. At a time when the world was content with using the Newcomen engine to pump water out of mines, Watt experimented with steam and was able to roughly double fuel efficiency. 

But simply inventing something revolutionary wasn’t enough. Watt had to find a way to make it appealing to the masses that were set in their ways. While it may have been easy to simply keep banging the fuel efficiency drum, it didn’t help his cause that not a lot of people used steam engines back then. 

The stubborn elders preferred to use draft horses to get things done - also known as cart or work horses. Watt realised he’d have to market his product better if he wanted it to go mainstream because evidently, hipsters weren’t cool back in the day. Changing people’s minds and making them try something new is never easy and Watt had to prove his invention to them in terms they would understand, so he got to work on more experiments. 

Since the populace was adamant on horses, Watt used them as a standard measure. He set about calculating the average productivity of one, determining how much power a regular draft horse could generate in a given period of time.

It took a while, but his calculations showed that an average horse could lift 33,000 pounds (15,000kgs) of material by one foot (0.3 metres) in one minute. With that, Watt created a new unit of measurement, and called it horsepower. 

Marketing to the rescue

The discovery of horsepower made no difference to the public, though. Why would they care about fancy nomenclature for scientific sorcery? To convince them, Watt used his findings to make an apples-to-oranges comparison between the horses and his machinery. He told them of how his engines could do the work of five horses in one go. 

His targeted marketing campaign worked and people flocked to invest in steam engines. However, Watt considerably overestimated the work rate of a horse - whether this was a stroke of luck or shrewd business tactics, who knows. In doing so, he made sure that his product would always over deliver.  

Watt’s steam engine went on to become a big player in the Industrial Revolution, but it’s his animalistic unit of measurement that’s surpassed it all, even the inventor himself.