How many watts is 1 horsepower?
1 mechanical horsepower (US automotive standard) equals 745.7 watts. The metric horsepower (PS, used in some European specs) is 735.5 watts.
Power calculator
Power converter
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Power is the rate at which energy is transferred or converted, measured in watts (W). 1 watt equals 1 joule per second. Common power units include the kilowatt (kW), megawatt (MW), horsepower (hp, where 1 mechanical hp = 745.7 W), and BTU per hour (1 BTU/hr ≈ 0.293 W).
Example power conversions
1 kW1,000 W, 1.34102 mechanical hp, 3,412.14 BTU/hr
1 MW10⁶ W, 1,341.02 hp, 3.412 million BTU/hr
1 mechanical hp745.6999 W, 2,544.43 BTU/hr (exact)
1 metric hp (PS)735.49875 W (exact), 0.98632 mech hp
Open the live power converter for any input value.
Watts and the SI power hierarchy
The watt is the SI coherent power unit, named for James Watt. 1 W equals 1 J/s, 1 V·A (volt-ampere) in DC electrical work, and 1 N·m/s in mechanical work. This compositional clarity makes it the universal scientific power unit.
Practical contexts span decimal prefixes from milliwatts (LED indicator lights) to kilowatts (household appliances, motorcycles) to megawatts (utility-scale generators, large industrial motors) to gigawatts (nuclear plants, regional grids). A residential rooftop solar system is typically 5-15 kW; a large wind turbine is 2-5 MW; a single nuclear reactor is 1-2 GW.
Horsepower: more than one definition
Horsepower is the most commonly cited non-SI power unit, but there are several incompatible definitions. The mechanical horsepower (550 ft-lbf/s, used in US automotive practice) equals 745.6999 W. The metric horsepower (75 kgf-m/s, used historically in Europe) equals 735.49875 W. The electrical horsepower (used in motor nameplate ratings) equals exactly 746 W.
The differences are small (under 2%) but real. A 200 mechanical hp engine is 149.14 kW; a 200 metric hp (200 PS in German specs) is 147.10 kW. For most casual use the distinction doesn't matter, but for accurate specs it pays to know which definition the source intended.
Power vs energy
Power and energy are commonly confused. Power is rate; energy is the cumulative quantity. A 1,500 W space heater has a power rating of 1.5 kW; running it for an hour uses 1.5 kWh of energy. The heater's power is fixed; the energy consumed depends on how long it runs.
On utility bills, the kilowatt-hour is the energy unit; the kilowatt is the power unit (used for peak demand charges in commercial pricing). Solar panels are rated in watts of peak output, but their annual energy production is in kWh. Always check which one you're being quoted.
Common power conversions
| From | Equivalent |
|---|---|
| 1 kW | 1,000 W, 1.34102 mechanical hp, 3,412.14 BTU/hr |
| 1 MW | 10⁶ W, 1,341.02 hp, 3.412 million BTU/hr |
| 1 mechanical hp | 745.6999 W, 2,544.43 BTU/hr (exact) |
| 1 metric hp (PS) | 735.49875 W (exact), 0.98632 mech hp |
| 1 electrical hp | 746 W (exact) |
| 1 BTU/hr | 0.293071 W (IT BTU) |
| 1 ton of refrigeration | 3,517 W, 12,000 BTU/hr |
| 1 ft-lbf/s | 1.35582 W |
| 1 W | 0.00134 mech hp, 3.412 BTU/hr |
Frequently asked questions
What's the difference between mechanical, metric, and electrical horsepower?
Mechanical hp = 745.7 W (US, defined as 550 ft-lbf/s). Metric hp / PS = 735.5 W (Europe, defined as 75 kgf-m/s). Electrical hp = 746 W exactly (used for motor nameplates). The three differ by about 1-2%.
How many BTU/hr is 1 watt?
1 W equals 3.412 BTU/hr. So a 1,500 W space heater outputs about 5,118 BTU/hr, which is useful for comparing electric and gas heating capacity.
What is a ton of refrigeration?
A ton (in HVAC) is 12,000 BTU/hr or 3,517 watts of cooling capacity. The unit dates to the rate of heat absorption when 1 short ton of ice melts over 24 hours.
How is power different from energy?
Power is the rate of energy transfer (joules per second, watts). Energy is the cumulative total (joules, kilowatt-hours). A 1.5 kW heater running for 2 hours uses 3 kWh of energy.