Horsepower Calculator

Horsepower is a measurement of power, or the rate at which work is done. This calculator can be used to compute horsepower according to its definition and to convert between different power units. To find the engine horsepower of a vehicle, please use our Engine Horsepower Calculator.

Horsepower Calculation Based on Definition

By definition, Power = force × distance / time.

Force: Distance: Time:

Horsepower Converter

Converts between different units of power.

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Horsepower

Horsepower is a unit of measurement of power developed by engineer James Watt in the late 18^th century. Although its original purpose was to compare the output of steam engines with the power of horses (hence its name), it has since been adopted as a unit of measurement for all sorts of engines used to power things such as vehicles, lawn mowers, boats, chainsaws, and airplanes.

Horsepower is commonly used today to refer to the potential work output of a vehicle's engine, and as such, is a widely cited measurement for performance comparisons. Although horsepower is an important metric for doing so, it should not be the only consideration in determining a vehicle's ability as there are other factors such as power-to-weight ratio, torque, drivetrain, and forced induction. For more information or to do calculations on vehicle horsepower, use the Engine Horsepower Calculator.

When measuring horsepower output of anything, to ensure precise comparisons between them, it is important to be consistent in the methodology used to determine horsepower.

Watt

Horsepower is not recognized in the International System of Units (SI); SI uses a measurement of power (a rate at which energy is generated or used) called a watt, which is named after James Watt. A watt is defined as one joule per second and is generally used to quantify a rate of energy transfer for lower rates of power consumption such as lightbulb or smartphone charging. On the other hand, kilowatts are commonly used for larger scale measures such as appliances and devices like refrigerators or servers. Energy is often presented using units of kilowatt hours (kWh), usually within the context of electric utilities delivering energy to household consumers.

BTU

The British Thermal Unit (BTU) is another unit of energy, and one unit of BTU is the amount needed to heat one pound of water by one degree Fahrenheit. Coincidentally, one BTU is also roughly the amount of energy released by burning one match. BTU is commonly used to compare the energy inherent in different fuels. 1 BTU is equivalent to 0.293 watt-hour or 1,055 joules.

Different Horsepowers

When the term horsepower is used, people are probably referring to mechanical horsepower. However, there are other lesser known definitions of the word.

Mechanical Horsepower, hp(I) — 550 foot-pounds per second, approximately 745.7 watts. The most common definition of horsepower, mechanical horsepower, is the horsepower James Watt invented in 1782.
Metric Horsepower, hp(M) — 75 kgf-m per second, approximately 735.499 watts
Boiler Horsepower, hp(S) — 34.5 pounds of water evaporated per hour at 212 degrees Fahrenheit, approximately 9,809.5 watts. This definition is mainly used to denote a boiler's capacity to deliver steam to a steam engine.
Electrical Horsepower — 746 watts. This definition is mainly used for electrical machines.

Frequently Asked Questions

How is horsepower calculated from force, distance and time?

Power is force multiplied by distance divided by time. One mechanical horsepower is 550 foot-pounds per second, or 745.7 watts, so a force of 10 newtons acting over 3 meters in 2 seconds produces 15 watts, about 0.02012 mechanical horsepower.

What is the difference between mechanical and metric horsepower?

Mechanical horsepower is 550 foot-pounds per second, approximately 745.7 watts. Metric horsepower is 75 kilogram-force meters per second, approximately 735.499 watts. Electrical horsepower is defined as exactly 746 watts.