The Confusing Difference Between American And European Horsepower

Sure, horsepower is one of the most recognizable metrics in the automotive industry, but how many drivers know that its meaning can change depending on where the car is sold? The United States and Europe both use "horsepower" to describe a vehicle's output, but the two measurements are not identical in every part of the world. It all falls back on James Watt, an 18th-century Scottish engineer who created the term while promoting his steam engine as a competitor to horses. Watt's calculation was based on assumptions about how much weight a horse could lift in a minute: It defined 1 horsepower as 550 foot-pounds of force per second. (To be clear: "1 hp" is not how much horsepower a horse actually has.)

Later, as the automotive industry grew, the United States kept Watt's unit of measurement while most of the rest of the world moved on to the metric system. This is where the split officially happened: with the creation of "metric horsepower" (see also: pferdestärke [PS] in Germany, or cavalli vapore [CV] in Italy). As it stands today, metric horsepower is about 1.4% lower than its American analogue. That means a vehicle with 100 PS in Europe would be equivalent to 98.6 horsepower in the States. It's only a slight difference, but it's enough to confuse buyers comparing specs across international borders.

For today's drivers, the distinction between U.S. and European horsepower shows up in some surprising ways. For example, when Bugatti unveiled its 1,000-horsepower Veyron, American magazines had to point out that the number was referring to metric hp. The official American rating was a slightly lower 986 hp. Likewise, the McLaren 765LT has 755 hp in U.S. terms, but is named for its 765 PS output.

Automakers can help underline the differences between the two by publishing multiple figures. They can cover electric vehicles at the same time, too. It's why you'll see many spec sheets now include power in kilowatts (kW), the International System of Units standard. One kilowatt equals 1,000 watts, and one U.S. horsepower equals 746 watts. That means a 100 kW electric motor produces 134 U.S. hp and 136 PS. Take the Porsche 911 Turbo S, for example: It's listed at 478 kW, 641 hp, and 650 PS, all of which tell you the same thing three different ways.

Will we see a future where horsepower — both its American and European definitions — comes second to kilowatts? It remains to be seen. For now, though, the horsepower debate remains relevant with each new gas-powered vehicle that hits the market. Another example: Audi recently announced its 2025 A5 and S5 lineup featuring turbocharged four-cylinder and six-cylinder engines. Outputs range from the mid-200s to over 350 hp, depending on configuration. In Europe, those numbers will be quoted in PS, meaning a figure like 370 PS would translate to roughly 365 hp on U.S. spec sheets. For car shoppers comparing reviews across different continents, the output might look inconsistent if you don't know the difference between the two.

It's why it's important to remember that while enthusiasts obsess over horsepower, it's only part of the full story. Torque, gearing, weight, and even aerodynamics have just as much of an influence on performance. Potential buyers looking at reviews for vehicles like the Audi A5, McLaren 765LT, or Porsche 911 Turbo S should look beyond horsepower to consider the other strengths of the cars. Maybe kW will become the new hp, or maybe it won't. But until a universal standard comes forward, we'll all just have to continue navigating this horsepower discrepancy from country to country.