How Power Unit Conversion Works
Power measures the rate at which energy is transferred or converted. The SI unit of power is the watt (W), where 1 watt equals 1 joule of energy per second. All other power units — horsepower, BTU/hour, foot-pounds per second — are fixed multiples of the watt, making conversion straightforward once you know the conversion factors.
This converter calculates all unit equivalents simultaneously. Enter a value in any unit and see the result across watts, kilowatts, megawatts, horsepower, BTU/hr, and foot-pound/second instantly.
Key Power Conversion Factors
- 1 kW = 1,000 W
- 1 MW = 1,000,000 W
- 1 mechanical horsepower = 745.7 W
- 1 BTU/hour = 0.29307 W (or 1 W = 3.41214 BTU/hr)
- 1 foot-pound per second = 1.35582 W
Horsepower Explained
Horsepower was defined by James Watt in the 18th century to compare the output of steam engines with the work capacity of draft horses. Today, multiple definitions of horsepower exist: mechanical (imperial) horsepower (745.7 W) is used for cars and engines in the US; metric horsepower (735.5 W) is used in Europe; and electrical horsepower (746 W) is used for electric motors. This calculator uses mechanical horsepower.
- Car engines: typically 100–500 hp (75–375 kW)
- Electric vehicles: 200–800+ hp (150–600+ kW)
- Household appliances: 0.5–5 hp (370 W–3.7 kW)
- Large industrial motors: hundreds to thousands of hp
Frequently Asked Questions
What is BTU/hr and when is it used?
BTU/hour (British Thermal Units per hour) is a unit of power commonly used in heating, ventilation, and air conditioning (HVAC). One BTU is the amount of heat required to raise one pound of water by one degree Fahrenheit. Air conditioners and furnaces are rated in BTU/hr or in tons of cooling (1 ton = 12,000 BTU/hr ≈ 3.5 kW).
What is the difference between power and energy?
Power is the rate of energy transfer (watts), while energy is the total amount transferred over time (watt-hours or joules). If a 1,000 W (1 kW) appliance runs for 1 hour, it uses 1 kWh of energy. Your electricity bill charges for kWh — energy — not watts — power.
How do I convert horsepower to kilowatts for an electric car?
Multiply horsepower by 0.7457 to get kilowatts. For example, a 300 hp electric motor produces 300 × 0.7457 = 223.7 kW. In Europe, electric car power is typically advertised in kW; in North America, it is often advertised in hp for familiarity.