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.
When you choose horsepower, this calculator will measure the approximate horsepower of an engine based on the torque of the engine (measured in foot-pounds) multiplied by the RPM of the engine, divided by 5,252 (conversion between foot-pounds and horsepower). For example, if your engine has a torque of 350 foot-pounds, then the horsepower would be 333 horsepower, at 5,000 RPM.
When you choose torque, this calculator will measure the approximate torque of an engine based on the horsepower, multiplied by 5,252 (conversion between foot-pounds and horsepower), divided by the RPM of the engine. For example, if your engine has 350 horsepower, then the torque would be 367 foot-pounds, at 5,000 RPM.
Horsepower
Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower.
Two common definitions used today are the imperial horsepower, abbreviated hp or bhp, which is about 745.7 watts, and the metric horsepower, also represented as cv or PS, which is approximately 735.5 watts. The electric horsepower, hpE, is exactly 746 watts, while the boiler horsepower is 9809.5 or 9811 watts, depending on the exact year.
The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses. It was later expanded to include the output power of other power-generating machinery such as piston engines, turbines, and electric motors.
The definition of the unit varied among geographical regions. Most countries now use the SI unit, the watt, for the measurement of power. With the implementation of the EU Directive 80/181/EEC on 1 January 2010, the use of horsepower in the EU is permitted only as a supplementary unit.
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.