If you are someone who is especially interested in automobiles, you must have heard the concept of horsepower. But you probably also think that one horsepower means one horsepower. Unfortunately this is not true…
Perhaps surprisingly, a horse can produce much more than a single horsepower. Estimates vary, but it is thought that a horse at full gallop can produce 12 to 14.9 horsepower.
What is horsepower?
Horsepower (hp) is a unit of power that describes the rate at which work is done. It is mostly used to measure the power of a car’s engine, but it is also possible to apply it to the power potential of an animal such as a horse.
In simplest terms, a single unit of horsepower is the amount of power required to move 249 kilograms (550 pounds) one step (about 30 centimeters) in one second, which equates to about 745 watts.
Horsepower as a unit of measurement was first devised around 1780 by Scottish engineer James Watt to compare the power produced by steam engines to a horsepower. Watt was a steam engine salesman and was looking for a way to promote his product to a largely horse-run market. By designing the horsepower unit, he was able to demonstrate the advantages of using the steam engine and persuaded manufacturers to leave their horses behind.
Using some imprecise calculations based on a single horse pulling a mill wheel for four hours, he calculated that the horse moves a load of 249 kilograms roughly one step per second. However, this is not a horse’s full potential and actually reflects the amount of strength a horse can continue to exert all day.
In fact, a horse’s peak mechanical power output is well above 12 horsepower.
This number comes from the work of two scientists who published an article in Nature in 1993 based on the observation that the maximum sustainable mechanical power per kilogram of muscle is 100-200 watts.
They estimated that a horse’s skeletal muscle is about 45 percent of its total mass, but they only use 30 percent of it when running. Considering a 600-pound horse, it could theoretically produce 18,000 watts of power. Since one horsepower is about 745 watts, that means 24 horsepower.
They also point out that this is probably an exaggeration. But they state that, based on decades of data collection, they think a healthy horse could possibly produce between 12 and 14.9 horsepower.
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