Perhaps surprisingly, a horse can pump out significantly more than a single horsepower. Estimates vary, but it’s thought a horse in full gallop could produce somewhere between 12 to 14.9 horsepower.
What is horsepower?
Horsepower (hp) is a unit of measurement of power that describes the rate at which work is done. It’s most often used to gauge 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 needed to move 249 kilograms (550 pounds) by one foot in one second, which is about 745 watts.
The unit was first conceived around 1780 by Scottish engineer James Watt to compare the output of steam engines to a workhorse. Watt was a seller of steam engines and he was looking for a way to promote his product to a market that was largely driven by horses. By devising the unit of horsepower, he was able to show the advantages of using the steam engine and convince mill owners to ditch their horses.
Through some fairly loose calculations based on a single horse pulling a mill wheel for four hours, he worked out that the horse was shifting roughly the equivalent of 249 kilograms (550 pounds) by one foot in one second. However, this is not the full potential of a horse and actually reflects the amount of power a horse can exert over a full day's work.
How much horsepower does a horse have?
In actuality, the peak mechanical power output of a horse is well over 12 horsepower.
That figure comes from a duo of scientists who published a paper in the journal Nature way back in 1993, based on the observation that the maximum sustainable mechanical power per kilogram of muscle is 100 - 200 watts.
They estimated that skeletal muscle for a horse is about 45 percent of the total mass, but they only use 30 percent of this while running. If we take a 600-kilogram (1,322 pound) horse, then it could theoretically produce 18,000 watts of power. Since one horsepower is around 745 watts, that would be 24 horsepower.
This, they wrote, is likely to be an overestimation. Citing some decades-old data, they believe that a fit horse could likely pump out between 12 to 14.9 horsepower.
“Collins and Caine list data from the horse pulling contest at the 1925 Iowa State Fair showing that peak mechanical power output of a horse is 12 - 14.9 horsepower. This effort lasted only a matter of seconds and is probably a realistic estimate of peak performance”, they wrote.