Power Unit Converter
Power is the rate at which energy is transferred or work is done. The SI unit is the watt (W), but engineers and technicians encounter many other power units in automotive, electrical, and HVAC contexts. This converter handles watts, kilowatts, megawatts, mechanical horsepower, metric horsepower (PS), BTU per hour, and kilocalories per hour. All factors follow NIST SP 811 and established engineering standards.
Power conversion factors (referenced to watt)
1 W = 0.001 kW = 1e-6 MW = 0.001341 hp = 0.001360 PS = 3.41214 BTU/h = 0.860421 kcal/h
Mechanical horsepower = 550 ft-lbf/s = 745.69987 W. Metric horsepower = 75 kgf-m/s = 735.49875 W. BTU/h factor uses the International Table BTU.
Power unit applications
- Watt / kW / MW: Electrical power generation, motor ratings, appliance consumption.
- hp (mechanical): US automotive engine power ratings, industrial machinery.
- PS (metric hp): European automotive power specifications (Germany, Japan).
- BTU/h: US HVAC equipment capacity: air conditioners, furnaces, boilers.
- kcal/h: Metabolic rate in nutrition; older mechanical engineering references.
Power unit converter: frequently asked questions
How many watts is one horsepower?
One mechanical (imperial) horsepower equals exactly 745.69987 watts. This is the US legal definition. Metric horsepower (PS or CV) equals exactly 735.49875 watts, which is slightly less.
What is the difference between mechanical and metric horsepower?
Mechanical horsepower (hp) = 550 ft-lbf/s = 745.69987 W. Metric horsepower (PS, Pferdestärke) = 75 kgf-m/s = 735.49875 W. European vehicle specifications typically use PS; US specs use hp. They differ by about 1.4%.
What does BTU/h measure?
BTU per hour (BTU/h) measures the rate of heat transfer. One BTU/h = 0.29307 W. It is the standard unit for HVAC cooling and heating capacity in the United States. A 12,000 BTU/h air conditioner equals 1 ton of cooling.
What is a kilowatt and how does it relate to kWh?
A kilowatt (kW) is a unit of power equal to 1,000 watts. A kilowatt-hour (kWh) is an energy unit: the energy consumed by 1 kW of power used for 1 hour. Power (kW) multiplied by time (hours) gives energy (kWh).
What is electrical horsepower?
Electrical horsepower is defined as exactly 746 watts by the US National Electrical Manufacturers Association (NEMA). It is used for motor ratings in the US electrical industry and is slightly more than mechanical hp (745.7 W).
Official sources
- NIST Special Publication 811: Guide for the Use of the International System of Units (SI).
- BIPM SI Brochure: The International System of Units.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.