Power Converter
Convert between watts, kilowatts, horsepower, and BTU/h
Power conversions are needed by electrical engineers sizing circuits, mechanical engineers comparing engine ratings, and HVAC designers calculating heat loads. Watts are the SI standard, but horsepower remains dominant in automotive contexts in many countries, and BTU/h is used for air conditioning and heating equipment. Understanding these conversions avoids costly mistakes when sourcing equipment or interpreting specifications from different markets.
Multi-Unit Converter
All conversions for 1 W
About Power Units
The SI unit of power is the watt (W = J/s). Electrical systems scale to kilowatts (kW) and megawatts (MW). Automotive power uses mechanical horsepower (hp, ≈ 745.7 W) or metric horsepower (PS, ≈ 735.5 W). Heating/cooling capacity uses BTU per hour (BTU/h). Boiler ratings use boiler horsepower (BHP).
History of Power Measurement
Power as a unit arose from the Industrial Revolution when James Watt needed to compare the output of his steam engines to the horses they replaced. He measured the work a horse could do per minute and defined horsepower as 33,000 foot-pounds per minute — a unit still in wide use for engines and motors. The watt, named after Watt, became the SI unit of power with the adoption of the metric system. Metric horsepower (75 kgf·m/s = 735.5 W) is slightly different from mechanical horsepower (745.7 W), and both differ from electrical horsepower (746 W), creating subtle but real differences in equipment specifications.
Practical Tips for Power Conversions
1 horsepower ≈ 746 watts, so a 200 hp car engine is about 150 kW. Electric motors and hybrid vehicles often list power in kW, while traditional engines use hp. For continuous electrical loads, 1 kW running for 1 hour consumes 1 kWh of energy. Converting between power and energy requires multiplying by the time duration — a common source of confusion. A 60 W light bulb running for 10 hours consumes 600 Wh = 0.6 kWh.
Common Pitfalls to Avoid
Mixing up horsepower definitions is common: mechanical (745.7 W), metric/DIN (735.5 W), electrical (746 W), and boiler (9,809.5 W) horsepower are all in use but not interchangeable. BTU and BTU/h are often confused — one is energy, the other is power. Watts and VA (volt-amperes) are equivalent for DC but differ for AC by the power factor, which matters for electrical equipment sizing. In three-phase electrical systems, power calculations must account for the factor of √3 when converting between line-to-line and phase voltages.
Professional Uses
Electrical engineers specify motors, generators, and power plants in kW or MW. Automotive engineers rate engines in hp and kW depending on market. HVAC designers size equipment in BTU/h or tons of refrigeration (12,000 BTU/h per ton). Mechanical engineers calculate pump and fan power requirements in kW or hp. Data center operators track power consumption in MW. Renewable energy engineers rate wind turbines and solar panels in kW or MW.