Watts to Horsepower Converter

How to use the watts to horsepower converter

1. Enter a value in the Watts field or the Horsepower field.
2. The other unit updates automatically as you type.
3. Read the converted result along with kilowatts and metric horsepower equivalents below.

How the watts to horsepower conversion works

The mechanical horsepower (also called imperial horsepower) is defined as exactly 745.699872 watts. To convert watts to horsepower, divide the wattage by that constant:

hp = W / 745.699872

For example, a 2,000 W electric heater produces 2000 / 745.699872 = 2.682044 hp. To go the other direction, multiply horsepower by 745.699872:

W = hp x 745.699872

This watts to horsepower formula applies specifically to mechanical horsepower, which is the standard used in the United States for engines and motors. Because the conversion factor is an exact definition rather than a measured approximation, the math introduces no rounding error on its own. Any loss of precision comes only from how many decimal places you choose to display.

Mechanical vs metric horsepower

Not all horsepower is the same. The two most common definitions are:

• Mechanical horsepower (hp(I)): Exactly 745.699872 W. Used in the US and UK for automotive and industrial ratings.
• Metric horsepower (PS, cv, ch): Defined as 75 kilogram-force meters per second, which equals approximately 735.49875 W. Common in Europe and Japan.

A 100 hp engine in the US produces about 74,570 W, while 100 PS in Germany produces about 73,550 W. This converter uses mechanical horsepower. If you need metric horsepower, divide watts by 735.49875 instead. Mixing up these two standards is one of the most frequent errors when comparing international vehicle specifications or selecting replacement motors for imported machinery.

Common power values reference

This table shows frequently encountered power levels converted between watts and mechanical horsepower.

When to use watts vs horsepower

Watts are the SI unit of power and appear on electrical devices worldwide. A toaster might be rated at 1,200 W, and solar panels are sold by their watt output. Horsepower remains the standard for internal combustion engines, electric motors, and pumps in countries that use the imperial system.

Engineers often need to switch between these units when sizing an electric motor to replace a gas engine, or when calculating the electrical input required for a given mechanical output. For related conversions involving torque rather than power, see the foot pounds to nm converter. Understanding both systems helps when reading datasheets from manufacturers in different regions.

Common mistakes in power conversion

The most frequent error is confusing mechanical horsepower with metric horsepower. Using 735.5 W instead of 745.7 W introduces roughly a 1.4 percent error, which matters in precision engineering. Another mistake is treating horsepower as a unit of energy rather than power. Power is the rate of energy transfer, so horsepower tells you how fast work is done, not how much total work is completed.

Also remember that engine ratings in horsepower usually refer to output at the crankshaft, while electrical ratings in watts may refer to input power. Efficiency losses mean a 1 hp motor draws more than 745.7 W from the wall. Typical AC induction motors operate at 80 to 90 percent efficiency, so a 1 hp motor might actually consume around 850 to 950 W of electrical power under full load.

Worked examples

Each result below was produced by the same code the tool runs, so you can check your own numbers against them.