The curious reason we measure horsepower

HP is a universally known and publicized measure of engine power, as well as the basis for countless vehicle purchasing decisions. However, despite the prominence given to it, very few people know for sure what is behind the term.

To understand the roots of this curious metric, you have to go back in time to the 18th century, when the advent of steam power was about to retire many hardworking horses.

Specifically, we have to go back to 1782, the year Scottish engineer and chemist James Watt coined the term as we understand it today in the automotive sector. The inventor was therefore trying to arouse interest in his new and improved version of the steam engine.

To do this, he had to prove the value of his product. It was there that he became interested in beasts of burden that pulled heavy loads in factories, mills and mines, in which he found a way to calculate the equivalent power of his new invention.

Thus, he would attract a lot of attention if he said that his steam engine produced up to 50, 80 or 100 horsepower.

Watt supervised a particular equine task. Attached to the spokes that radiate from the central axis of a mill, the horses revolved around it, drawing a circle seven meters in diameter, about 144 times in an hour, each pushing with an estimated force of about 75 kilos.

From this, the engineer calculated that one horsepower was equivalent to one horse exerting about 45,000 Nm of work in one minute. To better understand this, imagine a horse lifting a 15 kilo jug of water from the bottom of a 300 meter deep well in 60 seconds. This amount of work is equivalent to one horsepower.

Watt therefore used his newly invented power unit to compare the amount of work his stationary steam engine could do with that of a horse. It was the marketing magic he needed to convince companies that new technologies were the best source of energy.

This breakthrough, as we all know, revolutionized both industry and transportation, eventually leading to the rise of ships and steam locomotives.

In addition to power (HP), power can be offered in horsepower (CV) and kilowatts (kW). The latter are the official power unit of the International System of Units (SI), a measurement which, by the way, is gaining popularity among electric cars today.

Although it may seem like a trifle, the agreement of the international scientific community to use universal units of measurement meant a very important advance. And it is 1 meter, it measures the same here, in Spain, in Indonesia and on the surface of the Moon; during this time, that 1 second lasts the same in all the confines of the planet; and the same thing happens with kilos and mass.

That being said, the kW is a posthumous tribute to James Watt. Basically, the kilowatt is the Spanish version of the kilowatt. And for the record, 1,000 watts (or watts) equals 1 kW.

However, ironically, and despite the honor of bearing its name, 1 kW is not equal to 1 Hp, but to 1.34 Hp. Thus, to know the power of an electric motor – generally presented in kW in the technical sheet – in horsepower, simply multiply the kilowatts of the motor by 1.34. The result of this will be the HP.

The popularization of the electric car is increasingly talking about kilowatts to quantify power, both to talk about motors and for charging power. And that should certainly encourage us to adopt and widely use the kilowatt as a universal unit of power, both in electric vehicles and those with combustion engines.

This is not only more practical, but also more logical: 1 kilowatt is defined the same way for Europeans as for Americans, Asians and Chileans. The days of the steam engine are long gone; It’s time to talk about power in kilowatts.

So, for example, a 100 kW electric car motor is equivalent to 134 HP.