Horsepower Converter

Horsepower (hp) is a unit of power that measures the rate at which work is performed. Originally coined by Scottish engineer James Watt in the 18th century to compare the output of steam engines with the power of draft horses, horsepower has become the standard unit for expressing the power of engines and motors in automotive, industrial, and mechanical contexts worldwide.

One mechanical horsepower is defined as exactly 745.7 watts (or 550 foot-pounds per second). This value represents the power needed to lift 550 pounds by one foot in one second. While seemingly arbitrary, this definition provides a practical reference point that connects imperial and metric measurements.

There are several variations of horsepower used in different regions and industries. Mechanical horsepower (hp) is the most common in the United States and United Kingdom. Metric horsepower (PS or CV) is used in continental Europe and is slightly smaller at 735.5 watts. Brake horsepower (bhp) measures the power at the engine's crankshaft before losses from accessories and transmission.

Converting between horsepower and other power units requires knowing the conversion factors for each unit. The calculator uses these established relationships to provide accurate conversions between seven different power units.

The conversion process works by first converting the input value to a common reference (mechanical horsepower), then converting from that reference to the target unit. This two-step approach ensures consistency across all conversion paths.

This calculator supports conversion between seven power units with instant results:

1. Enter the power value: Type the numerical value you want to convert into the input field. You can enter whole numbers or decimals.
2. Select the source unit: Choose the unit of your input value from the "From" dropdown. Options include horsepower, kilowatts, watts, metric horsepower, brake horsepower, foot-pounds per second, and BTU per hour.
3. Select the target unit: Choose the unit you want to convert to from the "To" dropdown.
4. Use the swap button: Click the swap icon to instantly reverse the conversion direction, switching the "From" and "To" units.
5. View all conversions: Below the main result, the calculator shows the input value expressed in all seven units simultaneously, making it easy to compare across systems.

Horsepower (hp): The mechanical horsepower, also known as imperial horsepower, equals 745.7 watts. It is the most commonly used horsepower unit in the United States and United Kingdom for rating automotive engines and electric motors.

Kilowatts (kW): The SI-derived unit of power equal to 1,000 watts. Kilowatts are the standard unit for engine power in most countries outside the United States and are used in scientific and engineering contexts globally.

Watts (W): The SI base unit of power, defined as one joule per second. All other power units are defined as multiples or fractions of the watt.

Metric Horsepower (PS): Also called Pferdestärke (German for "horse power") or cheval-vapeur (French), this unit equals 735.5 watts — slightly less than mechanical horsepower. It is the standard in continental Europe, Japan, and many Asian countries.

Brake Horsepower (bhp): The power measured at the engine's output shaft before losses from the gearbox, alternator, and other accessories. For most practical purposes, bhp equals mechanical horsepower.

Automotive engineering relies on horsepower ratings to characterize engine performance. Car manufacturers specify maximum horsepower at specific RPM values, and understanding the conversion between hp and kW is essential for comparing vehicles across international markets where different units are used.

Electrical motor sizing requires converting between horsepower and kilowatts. Industrial motors are often rated in hp in the US but kW in metric countries. Engineers must convert between these units when sourcing equipment from international suppliers or designing systems for global deployment.

Aviation and marine engineering use various horsepower definitions depending on the application. Aircraft engines are typically rated in brake horsepower, while marine engines may use shaft horsepower. Converting between these units ensures accurate performance comparisons and specifications.