The power units
- Watt (W), kilowatt (kW) and megawatt (MW) are the SI units. One watt is one joule per second.
- Horsepower (hp) is defined as 550 foot-pounds per second, which is 745.69987 W.
- Metric horsepower (PS) is 75 kilogram-force meters per second, exactly 735.49875 W, about 1.4 percent less than hp.
- BTU per hour (BTU/h) is the international table BTU of 1,055.05585 joules per hour, about 0.2931 W. The BTU calculator finds the air conditioner size a room needs.
- Kilocalorie per hour uses the thermochemical kilocalorie of 4,184 joules, about 1.162 W.
The factors follow NIST Special Publication 811, Appendix B. In watts, each unit is:
| Unit | Watts | 1 kW equals |
|---|---|---|
| 1 horsepower (hp) | 745.6999 | 1.341022 hp |
| 1 metric horsepower (PS) | 735.4988 | 1.359622 PS |
| 1 BTU per hour | 0.2930711 | 3,412.142 BTU/h |
| 1 kilocalorie per hour | 1.162222 | 860.4207 kcal/h |
| 1 foot-pound per second | 1.355818 | 737.5621 ft·lbf/s |
How the conversion works
All power units are fixed multiples of the watt, so each conversion is one multiplication. To go from kW to hp, multiply by 1,000 and divide by 745.6999, which is the same as multiplying by 1.341022. From hp to kW, multiply by 0.7457. Between the two horsepowers, 1 hp is 745.6999 ÷ 735.4988 = 1.01387 PS, so hp to PS is × 1.0139 and PS to hp is × 0.9863. To turn the watts of an appliance into a running cost, use the electricity cost calculator.
- 300 hp to kW: 300 × 0.7456999 = 223.71 kW, which is 304.2 PS.
- 12,000 BTU/h to kW: 12,000 × 0.0002930711 = 3.517 kW.
- 2,000 W to BTU/h: 2,000 ÷ 0.2930711 = 6,824 BTU/h.
- 1,000 W microwave to hp: 1,000 ÷ 745.6999 = 1.34 hp.
- 250 W on a bike to hp: 250 ÷ 745.6999 = 0.335 hp, a third of a horsepower.
Engine power: kW, hp and PS side by side
Registration papers and spec sheets mix all three. The table lines them up for common engine sizes; the PS column is always about 1.4 percent above hp.
| kW | hp | PS |
|---|---|---|
| 50 | 67.1 | 68.0 |
| 75 | 100.6 | 102.0 |
| 100 | 134.1 | 136.0 |
| 110 | 147.5 | 149.6 |
| 150 | 201.2 | 203.9 |
| 200 | 268.2 | 271.9 |
| 250 | 335.3 | 339.9 |
| 300 | 402.3 | 407.9 |
Air conditioners and heaters: BTU/h to kW
Cooling and heating capacity is often sold in BTU per hour in one country and in kilowatts in another. Multiply BTU/h by 0.000293 to get kW, or divide kW by that number for BTU/h. The BTU calculator works out the size a room needs.
| BTU/h | kW | W |
|---|---|---|
| 5,000 | 1.47 | 1,465 |
| 8,000 | 2.34 | 2,345 |
| 12,000 | 3.52 | 3,517 |
| 18,000 | 5.28 | 5,275 |
| 24,000 | 7.03 | 7,034 |
| 36,000 | 10.55 | 10,551 |
These are rates of heat moved or produced, not necessarily the electricity drawn. On an air conditioner the cooling capacity and the power input are two separate figures on the label, so convert the one you need.
Common power conversions
| From | Equals |
|---|---|
| 1 kilowatt | 1.34102209 horsepower |
| 1 horsepower | 0.7456998716 kilowatts |
| 1 kilowatt | 1.359621617 metric horsepower |
| 1 metric horsepower | 0.9863200706 horsepower |
| 1 horsepower | 745.6998716 watts |
| 1 BTU per hour | 0.2930710702 watts |
| 1 kilowatt | 3,412.141633 BTU per hour |
Kilowatts to horsepower
| Kilowatts (kW) | Horsepower (hp) |
|---|---|
| 1 | 1.341 |
| 5 | 6.7051 |
| 10 | 13.41 |
| 50 | 67.051 |
| 75 | 100.58 |
| 100 | 134.1 |
| 110 | 147.51 |
| 150 | 201.15 |
| 200 | 268.2 |
| 250 | 335.26 |
| 300 | 402.31 |
| 400 | 536.41 |
| 500 | 670.51 |
How to use it
- 1Pick the unit you have on the left and the one you want on the right. kW to hp is set up when the page opens.
- 2Type the value. Either side accepts input, and swap turns the conversion around.
- 3Read the result and see the same power in every other unit in the list. Copy the number or a link.
Sources
- NIST Special Publication 811, Appendix B.9: horsepower, metric horsepower, BTU per hour and kilocalorie factors
- NIST Special Publication 811, Chapter 4: the watt as the SI derived unit of power
Frequently asked questions
How many horsepower is 1 kW?
About 1.341 horsepower. One horsepower is 745.7 watts, so divide the watts by 745.7, or multiply kilowatts by 1.341. A 110 kW engine has 147.5 hp, a 150 kW engine 201.2 hp.
What is the difference between hp and PS?
Horsepower (hp) is defined as 550 foot-pounds per second, about 745.7 W. Metric horsepower (PS) is 75 kilogram-force meters per second, exactly 735.49875 W, about 1.4 percent less. So 100 PS is about 98.6 hp, and 100 hp is about 101.4 PS. If a spec sheet quotes PS, the same engine shows a slightly bigger number than it would in hp.
How many watts is 1 horsepower?
About 745.7 watts, or 0.7457 kW. Metric horsepower is a little smaller, 735.5 watts. A 2,000 W appliance therefore draws about 2.7 hp.
How do I convert BTU per hour to kW?
Multiply by 0.000293071, or divide by about 3,412. A rating of 12,000 BTU per hour is about 3.52 kW. The other way, a 2,000 W heater gives off about 6,824 BTU per hour.
Is a kilowatt the same as a kilowatt-hour?
No. A kilowatt is power, the rate at which energy is used right now. A kilowatt-hour is energy, one kilowatt kept up for one hour. A 2 kW heater running for 3 hours uses 6 kWh, and that is what the electricity bill counts. Convert energy units with the energy converter linked below.