How this conversion works
Power is energy per unit time; one watt is one joule per second. Mechanical horsepower is defined as 550 foot-pounds per second, which is about 745.7 W. Metric horsepower (PS) is 75 kilogram-force meters per second, exactly 735.49875 W.
BTU per hour is common for heating and air conditioning. A ton of refrigeration is 12,000 BTU/h, the rate needed to melt one short ton of ice in 24 hours.
Formula: result = value × (base units per source unit) ÷ (base units per target unit)
Where this conversion is used
- Engine output quoted in hp, PS or kW.
- Air conditioner and heater capacity in BTU/h or tons of refrigeration.
- Appliance and solar panel ratings in watts and kilowatts.
- Comparing electric motor specifications across regions.
Worked example: 150 hp to kilowatts
- One mechanical horsepower ≈ 745.69987 W.
- 150 × 745.69987 = 111,854.98 W.
- Divide by 1,000: about 111.85 kW.
Unit definitions
| Unit | In watts | Note |
|---|---|---|
| Watt (W) | 1 | |
| Kilowatt (kW) | 1,000 | |
| Megawatt (MW) | 1,000,000 | |
| Milliwatt (mW) | 0.001 | |
| Horsepower (mechanical) (hp) | 745.699871582 | 550 ft·lbf/s ≈ 745.7 W. |
| Horsepower (metric) (PS) | 735.49875 | 75 kgf·m/s = 735.49875 W. |
| BTU per hour (BTU/h) | 0.2930710702 | |
| Foot-pound per second (ft·lbf/s) | 1.3558179483 | |
| Ton of refrigeration (TR) | 3,516.85284207 | 12,000 BTU/h. |
Horsepower to kilowatts
| Horsepower (mechanical) (hp) | Kilowatt (kW) |
|---|---|
| 1 | 0.7457 |
| 10 | 7.457 |
| 50 | 37.285 |
| 100 | 74.57 |
| 150 | 111.855 |
| 200 | 149.14 |
| 300 | 223.71 |
| 500 | 372.8499 |
BTU per hour to watts
| BTU per hour (BTU/h) | Watt (W) |
|---|---|
| 5,000 | 1,465.3554 |
| 8,000 | 2,344.5686 |
| 10,000 | 2,930.7107 |
| 12,000 | 3,516.8528 |
| 18,000 | 5,275.2793 |
| 24,000 | 7,033.7057 |
| 36,000 | 10,550.5585 |
Things to watch for
- Car specifications in Europe often use PS (metric horsepower), which is about 1.4% smaller than mechanical horsepower.
Precision and sources
Results are calculated from the definitions above and rounded to 12 significant digits; the converter shows up to eight decimal places and the tables four. Reference: NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B.
Frequently asked questions
How many watts is one horsepower?
About 745.7 W for mechanical horsepower and 735.5 W for metric horsepower.
How many BTU/h is a 1-ton air conditioner?
12,000 BTU/h, about 3.517 kW of cooling.