What Does Horsepower Have to Do With Horses?


Horsepower is something we hear a lot in advertising. Vacuums, lawnmowers, and pretty much anything that has a motor, come with a horsepower rating to show how powerful it is. It’s the automotive industry, however, that features it the most, since horsepower makes a huge difference in the vehicles we buy.

Even though we place a lot of value on the horsepower rating a car has, not everyone knows what it is and what it has to do with horses.

What is horsepower and where did it come from?

The term horsepower, surprisingly, came long before automobiles were even a thing. In the late 1700s, James Watt, a Scottish engineer, set out to improve on a steam engine design that he felt was inefficient. His new creation contained a separate condenser, air pump, and even a rotary apparatus.

The new design promised to be revolutionary to the mining and farming industries. But, getting prospective buyers on board with this new steam engine would not be easy.

People had always compared steam engines to horses before Watt’s creation came along. They originally replaced the use of horses so that production would increase by speeding up the process. Sellers would compare the power their engine would output by the number of horses it would take to perform the same task. The idea behind this, was that it would cost less to buy their machine then it would be to maintain several horses to do the same job.

To advertise his creation, James Watts took that same concept and created a new type of measurement to show how much power his steam engine had. Based on his research of horses, he came up with a figure of approximately 33,000 ft-lbs of work per minute for an average horse.

His unit of measurement wasn’t an exact scientific formula, but it was enough to make it believable, to prospective buyers, that one of his engines could perform the same amount of power as multiple horses.

How does it relate to cars?

The horsepower unit of measurement stuck. Over the years, other steam and piston engines continued to use it. Eventually, when automobiles started hitting the market, the same term became commonplace in advertising to show off how much power the car had.

Today, we measure horsepower by the amount of force needed to move 33,000 ft-lbs in one minute as Watts determined an average horse could do. The problem is that you could come up with several ratings, depending on certain factors.

However, to determine a more accurate number, a standard of measurement came out to regulate the output ratings. As Car and Driver explains, the official formula for power measurement is the SAE J1349.

With this method, you can get a third-party organization to certify the car as achieving the amounts you advertise it will do. This ensures consumers are getting what they paid for.

How does horsepower really affect cars?

Horsepower matters with the cars we buy. The higher the horsepower number is, the more advantage an automobile manufacturer has when selling a car with that motor, because speed is a desirable feature for many people. However, more factors go into achieving that speed. Why else would farm machinery have the same horsepower as a high-performance car?

For example, the amount of torque an engine outputs can impact the rating. Some other factors that affect a car’s performance include:

  • The weight of the vehicle
  • Body shape
  • Size of the engine
  • Type of motor (turbocharged engines have more to offer than standard)

But, not everyone is looking for a fast car. Lower horsepower outputs have benefits too. Smaller cars and midsize sedans will often sport a lower power rating to offer inexpensive price points. Not to mention, less horsepower typical means more fuel efficiency.

Even though we haven’t used horses for daily work for hundreds of years, horsepower ratings are still an important factor in a car’s performance. The rating you need for your vehicle’s engine should depend on what you want to get out of your purchase and which one meets your specifications.