Power is a fundamental engineering quantity that describes the rate at which work is done or energy is transferred. Two common units for expressing power in the United States and many industrial contexts are the electric horsepower (hp) and the kilowatt (kW). Understanding both units and how to convert between them is essential for selecting motors, sizing generators, and performing energy‑efficiency analyses.
What is a horsepower (electric)?
The electric horsepower, denoted as hpe, was originally defined to compare the output of electric motors to the mechanical horsepower used for steam engines. One electric horsepower is defined as exactly \(1\,\text{hp}_e = 0.746\,\text{kW}\). It is widely used in motor ratings, HVAC equipment, and pump specifications.
What is a kilowatt?
The kilowatt is the SI unit of power, equal to 1,000 joules per second. It is the standard unit in most scientific, engineering, and international trade contexts. Because the SI system is based on powers of ten, kilowatts simplify calculations and reporting, especially when dealing with large‑scale power systems.
Why convert between hp and kW?
- Equipment selection: Manufacturers often list motor power in hp, while utility bills and energy‑management software use kW.
- Regulatory compliance: Many energy‑efficiency standards require reporting in kilowatts.
- Cross‑border projects: International partners may use different units, necessitating clear conversion.
The conversion is straightforward because the factor is constant: multiply the number of electric horsepower by 0.746 to obtain kilowatts, or divide kilowatts by 0.746 to obtain horsepower.