Horsepower is a unit of power: how quickly an engine can do work. One mechanical horsepower equals 550 foot-pounds per second, or about 746 watts. More horsepower generally means a car can reach higher speeds and accelerate harder at high RPM.
Where the word “horsepower” came from
Scottish engineer James Watt created the unit in the late 1700s. He was selling improved steam engines to mine and mill owners who used horses to pump water and turn machinery. To show buyers what they’d get, he measured how much work a horse could do and set one horsepower as 33,000 foot-pounds per minute. That’s the same as lifting 33,000 pounds one foot in one minute.
Fittingly, the metric unit of power, the watt, is named after him.
Horsepower vs. torque
These two get confused all the time.
- Torque is twisting force: how hard the engine turns the crankshaft. You feel it as the push when you press the gas from a stop.
- Horsepower is how fast that twisting force is delivered. It’s torque multiplied by engine speed.
The formula in U.S. units is:
Horsepower = Torque (lb-ft) × RPM ÷ 5,252
That’s why torque and horsepower curves always cross at 5,252 RPM on a dyno chart that uses those units.
Types of horsepower you’ll see
| Term | What it means |
|---|---|
| Mechanical (hp) | 550 ft-lb/s, about 745.7 watts. Standard U.S. rating. |
| Metric (PS) | About 735.5 watts. Common in Europe, slightly smaller than hp. |
| Brake horsepower (bhp) | Measured at the engine’s crankshaft, before drivetrain losses. |
| Wheel horsepower (whp) | Measured at the wheels on a dyno. Lower than bhp due to drivetrain losses. |
| Kilowatts (kW) | Used for electric motors. 1 kW is about 1.34 hp. |
How much horsepower do you need?
For everyday driving, the power-to-weight ratio matters more than the raw number. A light compact car with 150 hp can feel quicker than a heavy truck with 250 hp. Torque at low RPM also matters more in daily driving than peak horsepower, which usually comes near redline.
Can a horse produce more than one horsepower?
Yes. A horse can briefly exceed one horsepower in a short burst. Watt’s figure was meant to describe steady work over time, not a horse’s peak effort.
Want more trivia like this? See our fun car facts list.
