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Horsepower is a standard measurement, whether you’re talking about a car or a shop vac, and the term is so commonplace that it’s easy to forget it has pre-vehicular origins. The term was coined by engineer James Watt (also namesake of the unit “watts”). As the story goes, while working with ponies in a coal mine, he estimated that an average horse could do 33,000 foot-pounds of work per minute. Watt lived from 1736 to 1819, so his work in horsepower predates the automobile’s beginnings in the late 1800s, though the same formula has been applied to measure the work potential of car engines and all kinds of machinery.

How Horsepower Relates to Engines

Watt’s horsepower formula is confusing, but there’s no need to understand it in order to understand why horsepower ratings affect cars. The reason car engines are measured in horsepower is because engines were invented, in part, to do the work that horses used to do, not because we need to know how much coal a car can move over a certain period of time. Horsepower is useful because it’s a consistent unit of measure, but a horsepower rating doesn’t tell us everything we need to know about an engine or a car’s performance. It just gives us an idea how that car’s power compares to the power of other cars.

Horsepower vs. Other Factors

Generally speaking, the more horsepower a car produces, the better its acceleration, which is a strong factor in its overall performance. That’s why car marketing talks a lot about the horsepower ratings of high-performance or best-in-class models. However, there are always other factors at work. If you drive a compact sedan and a large sedan with the same horsepower rating, the compact will be quicker because it is lighter. Torque is another engine spec the affects a car’s performance. It measures twisting force. The more torque a car has, the better it can accelerate from a stop and the more strength it has for towing. The engines in high-performance cars are tuned so that the horsepower and torque ratings complement each other and provide a well-balanced driving experience.

The Advantages of Lower Horsepower 

High-horsepower cars get a lot of attention. They’re stylish and expensive, fun to look at, fun to ride in, and fun to drive. Auto manufacturers are always trying to improve their horsepower ratings for a competitive advantage in the market. In light of constant conversation over the newest and highest-horsepower cars, it’s important to remember that cars with lower horsepower are worthy of consideration, too. Compact, small, and midsize vehicles don’t need a lot of horsepower; in fact, they’re usually better off without it. Modest horsepower ratings help keep these popular vehicles affordable, fuel efficient, and safe.

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Lower-horsepower cars can even offer distinct performance advantages over their more-powerful competitors. A favorite example is the 155-horsepower Mazda MX-5 Miata. This affordable rear-wheel drive roadster has a modest engine for a sports car, but the reason it’s fun to drive is because it’s light and agile – it’s not concerned with achieving the highest speed in a straight line. The Miata is a pretty simple car, and if its engine made much more horsepower, the dynamics would change considerably, and not necessarily for the better.

Horsepower and Acceleration 

To further illustrate the effects of horsepower on performance, let’s take a look at the Porsche 911 lineup. This luxury sports car comes in a bunch of different trim levels and is currently offered with several different engines, although certain trim levels are tuned so that the same engine has different horsepower ratings. The quoted zero to 60 mph times are straight from Porsche’s website (and to keep things simple and consistent, we’ll use the numbers as achieved with a manual transmission where possible).

The base engine is a twin-turbocharged 3.0-liter six-cylinder. It comes in the Carrera and Targa 4, where it makes 370 horsepower and accelerates from zero to 60 mph in 4.4 and 4.5 seconds, respectively.

In the Carrera S (4.1 seconds) and Targa 4S (4.2 seconds), this engine makes 420 horsepower. It also comes in the GTS (3.9 seconds), which makes 450 horsepower.

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The midrange engine is the 4.0-liter six-cylinder that comes in the GT3 RS (3.2 seconds) and the R (3.7 seconds), both of which are rated at 500 horsepower.

The top-of-the-line engine is a twin-turbocharged 3.8-liter six-cylinder. It comes in the Turbo (2.9 seconds) and Turbo S (2.8 seconds) and makes 540 and 580 horsepower, respectively. (These models aren’t available with a manual transmission; quoted times are with an automated manual gearbox.) 

Consider More Than Just Horsepower

The Porsche 911 model lineup shows clearly that as horsepower increases, cars accelerate faster and zero to 60 times go down. We’re talking fractions of a second, of course, and zero to 60 times don’t matter much in day-to-day driving, but there are few better, more objective ways to compare the performance of similar cars. While the entry-level Porsche 911 would probably be powerful enough to satisfy most buyers, there’s no doubt that the more-powerful and more-expensive models offer better performance.

While horsepower is important, it’s not the only factor to consider when buying a car. Shoppers should try out different engine types (for example, a turbocharged engine and a naturally aspirated engine have different driving dynamics, even if the horsepower ratings are similar), and buyers who value performance should remember that a well-rounded vehicle has good steering and handling to complement its acceleration.

More Tools From U.S. News & World Report

If you want to find out more about your favorite car’s horsepower rating and performance, head over to our new car rankings. Once there, you’ll be able to compare multiple vehicles and see which one suits your needs.

When you’re ready to buy, be sure to use the U.S. News Best Price Program to find the dealers in your area with the best prices. The BPP helps save shoppers an average of $3,279 off their new car purchase.