Horsepower vs. Torque: What’s the Difference?

Though most can comprehend the general premises of horsepower and torque, their definitions, their history, their applications, the mathematical equations used to find their values, and how and why manufacturers use each, aren't as well known. And, understandably, searching Google to ascertain those differences can be, well, ridden with potential errors, erroneous details, and old-timey baseball references only Boomers would know. 

With help from our team of info experts, we’ve concocted the end-all-be-all guide to horsepower vs. torque. We explain not only what each is and how they’re used, but also the different measurements of each.

A horsepower is a unit of measurement used to denote power or the “rate at which work is done” by an engine or motor. This applies to all engines and motors and not strictly internal combustion engines. Your car’s horsepower denotes how quickly that work can be done with more power allowing for quicker work.

Torque is force multiplied by distance. In the case of cars, “the rotational equivalent of linear force.” Essentially, it’s the amount of force applied to an object with a twisting motion, i.e. a motor applying force to a crankshaft, which consequently rotates your tires. 

The two are very much two sides of the same coin as one goes with the other—torque being the force and horsepower being the rate at which that force is done. The difference is torque is doing the work, while horsepower is how fast that work is being done. 

Horsepower and torque, along with where each falls on a vehicle’s engine rotation per minute (rpm) range, as well as gearing, determine the car’s speed and acceleration.

We can thank the Scottish engineer James Watt for the origins of horsepower. He was looking to compare the output of steam engines and draft horses in order to sell people on his steam power business. Steam engines were new, horses were not. By relating his engine's power to that of our equine friends, he figured people would better understand what his machines were capable of. Observing a horse could turn a mill wheel 144 times per hour, and that the wheel had a 3.7-meter radius, Watt determined the horse could travel 2.4 × 2π × 12 feet in one minute.

Here’s the equation for all you math nerds.

P=Wt=Fdt=180lbf x 2.4 x 2 x 12ft1min=32,572ft lbfmin

Watt could then apply this formula to his steam engines and determine how much more effective they were compared to the horses everyone used at the time. It's worth noting that horsepower is a continuous figure. Like many other types of tractive engines—biological or mechanical—horses can output more than a single horsepower at peak. They can, however, often only maintain around one horsepower continuously.

There's a laundry list of labels and measurements used to advertise power output. For torque, automotive manufacturers use pound-feet (lb-ft), foot-pounds (ft-lbs), and Newton meters (NM). 

A pound-foot is the moment of inertia on an axis that applies one pound of force at a radius of one foot.

Foot pounds is the British version of pound-feet. Foot-pound also refers to a unit of work, the same as pound-feet, but it has been co-opted by auto manufacturers. 

A newton-meter is a unit of torque in the metric system. It's equivalent to one Newton applied at a radius of one meter. One foot-pound is equal to 0.73756 newton meters. 

As with torque, there’s differentiation between manufacturer-supplied figures representing horsepower, with the main four being horsepower, brake horsepower, metric horsepower, and kilowatt. Here’s what they all mean and why they’re used. 

Horsepower is the most commonly used figure to denote a car’s power and most often relates to how much power a car’s engine develops at the engine's crankshaft, not at the tires. It’s easy, it’s known, and it looks great splashed across marketing. 

Brake-horsepower is commonly used by countries outside the U.S. It typically denotes the engine’s power with more accessories than their American counterparts. A car may, for instance, have a power steering pump or air conditioning compressor that's not essential to the engine running but is essential to the car functioning as the manufacturer intended. American manufacturers will sometimes dyno an engine without these components, which can lead to slightly higher power figures.

It must be said that this difference is usually minimal and as the auto industry electrifies, it will become less relevant.

One metric horsepower, whether written as pferdestärke (PS), cheval-vapeur (CH), or cavallo vapore (CV), differs from an imperial or standard horsepower due to how it was calculated. To obtain a metric horsepower, a horse was attached to a 75-kilogram weight on the end of a pulley and was then timed as to how quickly it could lift it by one meter. The result is one second. This equation was then made to equal one metric horsepower, which is actually 98.6 percent of an imperial or standard horsepower when compared. 

Metric and American horsepower are often so closely related that it makes no practical difference to cite both of them. 300 American horsepower translates into around 304 metric horsepower. That's the kind of difference a dirty air filter or ambient temperature could easily produce. You can read them as effectively the same.

Here’s the math for you lovers of equations!

75 kg × 9.80665 m/s2 × 1 m / 1 s = 75 kgf⋅m/s = 1 PS

Kilowatt is a term our friends down under use most frequently. It's kinda the purest measurement of power on this list, consisting of 1,000 watts. One kilowatt equals 1.341 standard horsepower, which translates into one horsepower being about 735 watts. It's often easier to round that to 750 for the sake of a simple conversion.

Kilowatts are becoming more popular globally as a measurement of power due to electric vehicles' growing prevalence. Charging speeds, for instance, are often measured in kilowatts.

The output of combustion engines is not often measured in watts; however, that's not the case with electric drivetrains. Wattage is just a measurement of power. In the case of electric vehicles, that's simply the current in amps multiplied by the voltage. It therefore a lot of makes sense in EVs to measure power, whether it's at the "crank" or coming from the plug, in kilowatts.

A: One is not necessarily better than the other. Internal combustion engines are rated at peak torque and peak horsepower. Peak torque represents the point where the engine is working most efficiently. Peak horsepower is where the engine is producing the most power irrespective of efficiency. If you want a good tow vehicle, for instance, you want that peak efficiency at low engine speeds for a variety of reasons. If you want a good race car, torque is often less relevant, as chasing power is key.

The two figures are too closely related to really make any sort of direct comparison. How these forces are perceived has more to do with the shape of each curve over the engine's operating RPM than the actual peaks.

A: Horsepower is effectively a more relevant figure for most street cars. Torque is relevant, but horsepower is applied torque. If you have torque but can't apply it at higher engine speeds, you won't have much power and won't be able to take advantage of it in a high-performance, high-speed situation.

A: This is a rabbit hole. Electric cars deliver power differently as compared to internal combustion engines and do not necessarily have more torque just as a matter of fact. Most EVs use permanent magnet motors which turn electrical energy from the battery into mechanical rotation. All permanent magnet motors, if given power from an appropriately sized battery through an efficient inverter, will deliver power and torque the same way. The power and torque curves pretty much always look the same, just at different amplitudes depending on the current/voltage. Just because of the way this curve is shaped and the very nature of electric motors, EVs have all of their torque from zero RPMs, but not all of their power.

Going back to how the shape of the curve influences how a car feels, this translates into EVs generally feeling faster than they are, since they can apply such high torque at such low wheel speeds. The actual power of these engines feels closer to their ICE counterparts at highway speeds, where most PM motors tend to see a considerable loss of torque. So no, EVs do not naturally have more torque than ICE engines, they just deliver it differently which makes them feel like they have more.

The fact of the matter is that there's nuance to this entire conversation that's easy to lose in casual conversation. Torque and horsepower are related. When you're driving a car, you feel both of them. More than anything else, the shapes of the curves will have more to do with a car feeling "torquey" or "peaky" than the actual maximum figures.

Whether you want a car that has more torque or horsepower depends on the application. For heavy trucks, torque at low RPM is important. For something like a Honda S2000, the entire point is that it's more fun to squeeze out that power at higher engine speeds. In the end, torque versus horsepower depends on the application. One is not better than the other in every situation.