Horsepower is the standard way people talk about car performance, but it was never really designed for cars. The unit was created in the late 18th century by Scottish engineer James Watt as a sales tool for static steam engines. It wasn’t a direct measurement of engine output — it was a bit of math meant to give mine owners a rough idea of how many horses a steam engine could replace. Over two centuries later, it’s still used to compare everything from hatchbacks to hypercars, even though the logic behind it doesn’t apply to moving vehicles.
How horsepower became the universal car metric
Watt didn’t invent horsepower. He formalized it. In 1782, he watched brewery horses working and calculated what an average horse could sustain over a full working day. That number — one horsepower — was deliberately lowballed to make steam engines look like a good deal. A fit horse can actually produce around 15 horsepower when working hard, but Watt wasn’t looking for accuracy. He was looking to sell engines.
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The calculation made sense for static engines that chugged away at constant load all day. Mining entrepreneurs needed to know how much coal could be moved from the bottom of a shaft to the top, and how fast. Horsepower gave them a number they could understand.
But cars don’t work like that. An automotive engine isn’t designed to run at maximum load for eight or ten hours straight. That kind of test would destroy most modern engines — they’d overheat, break, or catch fire. The article uses the example of a heavily loaded Land Rover Defender Octa driven at a steady 6,000 rpm for a full workday. Even with the best engineering, it would fail. That’s not a fair test of what a car is meant to do.
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Why the wrong measure stuck around
Despite being misapplied, horsepower has become the closest thing to a global currency for car performance. Nobody gets excited about 883 kilowatts of peak power. But say a car has 1,184 horsepower, and enthusiasts know what that means. It’s romantic, even if it’s not really accurate. The idea of a thousand invisible horses pulling a Ferrari F80 is appealing. But it’s fanciful.
Torque and engine speed are the actual physical outputs of an engine. Horsepower is just torque multiplied by engine speed, then adjusted with a constant. It’s an interpretation. But it’s the number that sells cars. Watt’s original “translational marketing” still works.
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A strange historical accident
The persistence of horsepower is a historical accident. Vehicle engines have always deserved their own convention for measuring power output. Changing that now would be almost impossible. The auto industry, the media, and car buyers all rely on the same familiar number. Many efforts from engineers to move to kilowatts or other metrics have gained little traction outside technical circles. The standard remains horsepower — a notional figure from the 18th century, based on a brewery horse, still used to judge the fastest cars on Earth. The article suggests it’s probably best just not to think about it too much. The romance of the number might be worth more than the math.