Power Converter
This power converter changes a value between ten units of power: watts, kilowatts, megawatts, mechanical horsepower, metric horsepower (PS), BTU per hour, kilocalories per hour, foot-pounds per second, refrigeration tons and calories per second. Pick the unit you have and the unit you want, and a table below the result shows the same power in every unit, so you can compare an engine rating, an air conditioner label or a heater spec at a glance.
Updated
Results
- Unit
- Power in watts (W)
| Unit | Value |
|---|
Results are estimates. See the methodology below.
How to use the converter
- Enter the value. Decimals are fine, for example 1.5 or 0.746.
- Choose the unit you are converting from, such as hp.
- Choose the unit you want, such as kW.
You get the converted value, the target unit and the same power in watts. The table lists the value in all ten units, which is the quickest way to answer questions like “how many BTU/h is my 3.5 kW mini-split?” without changing the selects again.
Conversion factors
Every conversion goes through the watt (W), the SI unit of power, equal to one joule per second: the value is multiplied by the factor of the source unit and divided by the factor of the target unit. The factors follow NIST Special Publication 811, Appendix B.
| Unit | Definition | Watts |
|---|---|---|
| kW / MW | 1,000 W / 1,000,000 W | exact |
| hp (mechanical) | 550 ft·lbf/s | ≈ 745.6999 |
| PS (metric horsepower) | metric horsepower | 735.49875 |
| BTU/h | International Table BTU per hour | ≈ 0.2930711 |
| kcal/h | International Table kilocalorie (4,186.8 J) per hour | 1.163 |
| ft·lbf/s | foot-pound-force per second | ≈ 1.355818 |
| TR (refrigeration ton) | 12,000 BTU/h | ≈ 3,516.853 |
| cal/s | thermochemical calorie (4.184 J) per second | 4.184 |
Note that kcal/h and cal/s use different calories, matching how each unit is usually defined; the two calories differ by less than 0.1%. Results are shown to 12 significant digits.
Examples
1. One horsepower in every unit
| Unit | 1 hp equals |
|---|---|
| W | 745.70 |
| kW | 0.7457 |
| PS | 1.0139 |
| BTU/h | 2,544.43 |
| kcal/h | 641.19 |
| ft·lbf/s | 550 |
| TR | 0.2120 |
| cal/s | 178.23 |
2. Car engines: kW, hp and PS
An engine rated at 150 kW makes 201.15 hp. A 100 kW engine is 134.10 hp but 135.96 PS, because the metric horsepower is about 1.4% smaller than the mechanical one. Going the other way, 300 hp is 223.71 kW, and 100 PS is 98.63 hp.
3. Air conditioners and heaters
A 12,000 BTU/h window unit is exactly 1 refrigeration ton, or 3,516.85 W of cooling. A 24,000 BTU/h (2-ton) system moves 7.03 kW of heat. A mini-split labeled 3.5 kW is 11,942.50 BTU/h, and a 1,500 W space heater puts out 5,118.21 BTU/h of heat.
Horsepower, PS and electric horsepower
Three horsepowers are in common use. Mechanical horsepower (hp), defined as 550 ft·lbf/s, is what “hp” usually means in the US. Metric horsepower, written PS, CV or ch, is about 735.5 W. Electric horsepower is exactly 746 W; enter 746 W and convert to hp and you get 1.0004, so for most purposes the two are interchangeable. Boiler horsepower, about 9,809.5 W, is a different, much larger unit and is not included here.
On cooling equipment, BTU/h and kW measure the heat the unit removes, not the electricity it draws. The ton dates from the ice era: melting a short ton of ice over 24 hours absorbs roughly 12,000 BTU per hour.
Frequently asked questions
How many watts is 1 horsepower?
One mechanical horsepower is about 745.7 W (0.7457 kW). One electric horsepower is exactly 746 W, and one metric horsepower (PS) is about 735.5 W.
How do I convert kW to hp?
Divide by 0.7457, or multiply by about 1.341: 100 kW = 134.10 hp. For metric horsepower multiply by about 1.36: 100 kW = 135.96 PS.
What is the difference between hp and PS?
PS (Pferdestärke) is the metric horsepower, about 735.5 W. The mechanical hp is 550 foot-pounds per second, about 745.7 W. 1 hp = 1.0139 PS.
How many BTU/h is a ton of air conditioning?
One refrigeration ton is 12,000 BTU/h, about 3.52 kW. A 3-ton central air system is therefore rated at 36,000 BTU/h.
Does a 12,000 BTU air conditioner use 3,500 watts of electricity?
No. 12,000 BTU/h (3,516.85 W) is the cooling output. The electrical input is typically much lower, because an air conditioner moves heat rather than producing it; the ratio is its efficiency rating, shown on the label.
How do I convert watts to BTU per hour?
Multiply by about 3.412: 1 kW is 3,412.14 BTU/h and 1,500 W is 5,118.21 BTU/h.
Sources
Conversions use the standard factors listed on this page and are rounded for display. Equipment ratings depend on the test standard used by the manufacturer.