Power Converter
Convert power into kW, W, PS (metric horsepower) and hp (mechanical and electric horsepower) at once.
Power units and their definitions
The size of each unit in watts is listed below. The converter first turns your value into watts, then divides by the size of each unit.
| Unit | Size of one unit | Definition and source |
|---|---|---|
| Watt (SI) | ||
| MW (megawatt) | 1,000,000 W | 1,000,000 W (SI prefix mega) |
| kW (kilowatt) | 1,000 W | 1,000 W (SI prefix kilo) |
| W (watt) | 1 W | The SI unit of power: one joule per second |
| mW (milliwatt) | 0.001 W | 1/1,000 of a watt (SI prefix milli) |
| Metric horsepower (PS) | ||
| PS (metric horsepower) | 735.5 W | Used here as an approximation: exactly 735.5 W. NIST lists "horsepower (metric)" as 7.354 988 E+02 W = 735.4988 W (not marked exact), so the value used is 0.0012 W (about 0.00016%) larger. Not the same as the mechanical horsepower. NIST SP 811, NIST SP 811, Appendix B.9 |
| Mechanical horsepower (hp) | ||
| hp (mechanical horsepower) | 745.69987158227022 W | 550 foot pounds-force per second, worked out as about 745.699872 W from the foot, the pound and standard gravity (9.80665 m/s²). NIST lists 7.456 999 E+02 W.. NIST SP 811, NIST SP 811, Appendix B.9 |
| Electric horsepower (hp) | ||
| hp (electric horsepower) | 746 W | Exactly 746 W (NIST lists 7.46 E+02 W as an exact factor). NIST SP 811, NIST SP 811, Appendix B.9 |
The calculation uses exact fractions, and the only rounding is the one applied when a value is displayed.
The three horsepower units are different units
- PS (metric horsepower) = 735.5 W, used here as an approximation. The calculation uses exactly 735.5 W. NIST SP 811 (Appendix B.8 and B.9) lists "horsepower (metric)" as 7.354 988 E+02 W, which is 735.4988 W, and does not mark it as exact. The value used here is 0.0012 W larger than the NIST figure, a difference of about 0.00016%, so results in PS are very slightly different from the NIST factor. The value 735.5 W is the one this tool has used since it was first published in Japan, where it is the figure fixed in the national measurement-unit order. If you need the more exact metric horsepower, use the NIST figure above.
- hp (mechanical horsepower) = 550 foot pounds-force per second = about 745.6999 W. Worked out from the foot (0.3048 m), the pound (0.45359237 kg) and standard gravity (9.80665 m/s²). NIST lists 7.456 999 E+02 W.
- hp (electric horsepower) = 746 W. NIST lists 7.46 E+02 W as an exact factor.
PS and hp are different units even though both are called "horsepower" (1 hp is about 1.0139 PS, a difference of about 1.4%). When a figure is given only as "horsepower", check which one is meant. This tool keeps the three in separate groups and converts between them.
NIST SP 811 also lists boiler, U.K. and water horsepower. They are not included here.
Examples
- 1 PS = 735.5 W = 0.7355 kW
- 1 hp (mechanical) = about 745.6999 W = about 1.01387 PS
- 1 hp (electric) = 746 W
- 100 PS = 73.55 kW = about 98.63 hp (mechanical)
- 100 kW = about 135.96 PS = about 134.10 hp (mechanical)
- 200 hp (mechanical) = about 149.14 kW
- 1 kW = 1,000 W = 1,000,000 mW
Notes
- You can enter decimals (up to 12 digits before the decimal point and 6 decimal places). Use a period as the decimal separator. Commas are accepted only as thousands separators, for example 1,234.5. Negative values cannot be entered.
- Power (energy per second) and energy (an amount) are different quantities. To convert J, Wh, kWh and kcal, use the Energy Converter.
- For the relation between voltage, current and power, see the Ohm's Law Calculator. For watt-hours in a battery, see the Battery Capacity Calculator.
- The conversions are for reference. For engine ratings in a specification or a contract, check which horsepower and which test standard the figure refers to.
Sources
The definitions on this page come from the sources below (checked on November 1, 2026). The horsepower rows of NIST SP 811 Appendix B.8 and the POWER section of Appendix B.9 were read word for word. Appendix B marks exact factors in boldface. The text of the footnotes that some rows refer to was not needed for these rows and was not read for them.
- NIST Special Publication 811, Appendix B.8: Factors for units listed alphabetically
- NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity or field of science (pressure or stress)
Frequently asked questions
How many kW is one PS?
0.7355 kW (735.5 W), the value this tool uses for metric horsepower.
Are PS and hp the same?
No. 1 hp (mechanical) is about 745.7 W and 1 PS is 735.5 W, a difference of about 1.4%.
How many horsepower is 100 kW?
About 135.96 PS in metric horsepower, or about 134.10 hp in mechanical horsepower.
What is electric horsepower?
A unit that sets 1 horsepower at exactly 746 W (NIST SP 811). It differs slightly from the mechanical horsepower (about 745.7 W).