What Exactly Is Horsepower?

Throughout the history of automobiles, the measurement of power that an engine (and, in turn, a vehicle) can produce has become a central focus. Even after the first steam-powered machines were conceptualized and introduced in the 17th Century, contentious individuals who were objective of the capabilities of man-made devices decided to voice their opinions on the matter. Unless there was some form of guarantee that the engines could outperform traditional means of utility, they would remain skeptical of the admittance of locomotive machinations into their daily lives.

As with most revelatory discoveries made throughout human history, a number of gifted minds came forward to propose their own hypotheses regarding the output of the newly devised powerplants. At the time, a commonly used form of transportation, the horse, seemed to be the most “comfortable” comparison, allowing these individuals to provide an enticing differentiation between the trusted equestrian that had helped to drive humanity’s progression for centuries, and the daunting steel (and iron) monstrosities that were to replace them. Below, we’ll run through a brief history of the figure known as “horsepower,” a measurement that’s helped to define the controversial power associated with humanity’s mechanical platforms, and one that has stoked the competitive nature in the world’s most prolific automotive manufacturers, to boot.

The History Of Horsepower

Humble Beginnings

The first steam-powered engine — a crude and inefficient machine that was devised to evacuate water out of coal mines during the most adverse times of the year — was built in 1698 by England’s Thomas Savery. Though inefficient in its use of materials and constituent power, the machine utilized vast amounts of coal (and no moving parts) to aid in the movement of water from flooded mine shafts, back to the surface. Over the next 100 years, the machine would be revised only a handful of times, with the final iteration falling upon the shoulders of James Watt, a Scottish engineer who saw a great opportunity in both Savery’s (and later, Thomas Newcomen’s) intermediate design. While Savery and Newcomen saw no grander purpose for their steam-powered pump, Watt found their discovery fascinating and searched for a way to improve upon the original. In 1763, he embarked on an intellectual journey that would revolutionize mechanical output, reimagining the machinations of his predecessors through the use of a cylindrical “crankshaft” that housed a forward- and backward-moving piston. Throughout its range of motion, this piston would create a circular movement, giving birth (albeit, unknowingly) to one of the earliest versions of the locomotive.

By 1776, Watt had partnered with an English manufacturer to fund the construction of the first full-fledged steam engine and had spent a large portion of his time (and funds) thinking of ways to market the new technology to insistent farmers and miners. For hundreds of years, these individuals had relied on their own tenacity, guile, and livestock to help them navigate the challenges of everyday life — making it all the more difficult for Watt to convince them that the future was an informed investment, and not a mischevious plot to rob them of their livelihoods. One animal, in particular, was an irreplaceable ally to society — the powerful, four-legged equestrian. As a single entity, the workhorse could plow, pull, lift, and traverse — giving it exemplary standing as the quintessential utilitarian livestock throughout humanity’s longrunning history. The problem, however, were the costs associated with the upkeep of large communities of these animals. Feed, water, provisionary healthcare, and the need to retire/employ new horses after years of tumultuous work, were seen as necessities for their ownership — but not for James Watt. As part of his then-ludicrous plan to replace mankind’s dependable companion, he needed a way to market his new steam-powered invention, a way to measure its output, and a way to put an end to the dispute of unfounded claims of power, once and for all.

To confound the general public’s reticence toward his machinations, Watt decided to observe the animals he hoped to replace while they were in their natural state. He estimated that the carrying, pulling, and lifting capabilities of a pony averaged around 220 lbf (pound-force) at 100 ft. per minute (220 lbf x 100ft./min. = 22,000 lbf x ft./min.). Further, he concluded that a horse, being 50% larger and more robust than a pony, could output a tangential amount of power. To test his hypothesis, he procured a workhorse at peak health, tethered it to a mill wheel, and coerced it to rotate the wheel, while maintaining a steady pace, for one hour. He found that, within the hour, the horse could turn the mill wheel 144 times, or 2.4 times per minute. Since the wheel was 12 feet (3.7 m) in radius, Watt defined the power of the horse (over one minute) using this formula: 2.4 × 2π × 12 feet, with an estimated “force of pull” at (or near) 180 pounds-force (800 N).

Referencing the information he had surmised prior to the experiment, Watt found that the horse’s capability was equal to, or greater than, 32,572 ft⋅lbf/min, which he opted to round upward — finalizing his measurement at an even 33,000 ft⋅lbf/min. This figure would become known as “horsepower,” and would be used throughout his future marketing endeavors. Alongside the prospect of a machine that would produce as much power as a single horse (or, to be more accurate, several horses), Watt prospered under the guise of humility, stating that workers would no longer have to worry about the housing, cost, and upkeep of livestock. Needless to say, the mechanical inventions that he and his colleagues solicited began to make waves within society, and it wasn’t long before the transition from horse-drawn utility to that of steam-powered productivity, took place. Eventually, other forms of mechanized technology would call upon Watt’s renowned formula for in their own measurements of power.

How Horsepower Is Utilized Today

Modern Application

With horsepower being utilized as the first metric for potential power output, it makes sense that it was adopted by the very first vehicle manufacturers to provide a basis for measurement in regards to engine power. From consumer vehicles to the most promising hypercars, the understanding of “horsepower” has helped to shape, define, and sanctify the approach that automakers take when it comes to their newly devised platforms. As with every adolescent formula, the horsepower that was referenced in Watt’s era has been fine-tuned for a number of different applications, including hydraulic, electric, and metric uses — giving manufacturers a way to benchmark their various tools and innovations. Overall, there are around eight different types of horsepower, but we’ll focus on the primary unit of measurement, mechanical horsepower, below.

Taking what we know from Watt’s initial measurement of horsepower, we understand that, in order to move 33,000 pounds one foot in a minute, the force needed to move 550 pounds one foot in a second can be applied to the weight of a traditional chassis, as well as the engine it houses. To the chagrin of many, modern horsepower is actually calculated using a dynamometer (or dyno, for short) — a device that measures both the torque and rotational speed (RPM) of an engine so that its instantaneous power can be regulated. In short, torque is the primary basis for the measurement of horsepower. In the grander sense, torque can be defined as torsional (or twisting) force measured in units of force times distance from the axis of rotation. To break it down into simpler terms, these two variables are recorded by the modern-day dynamometer and can be defined through implementation within the following formula: Torque x RPM / 5,252 — a diagnostic equation that helps manufacturers to provide a grounds for competitive power ratings.

The horsepower that a vehicle exerts is almost always synonymous with the amount of torque that it’s able to produce, translating directly into the car’s overall speed. Though this is vastly trivialized by the type of differential (and transmission) that the vehicle boasts, the measurement of horsepower has become the primary selling point for the world’s most powerful platforms — whether they be auto, moto, land-faring, or aquatic — since Watt’s discovery all those years ago.

12 Best AWD Supercars

Now that you know where the basis for horsepower comes from, take a look at our guide on the best AWD supercars to get a better feel for how all those ponies are put to use.