hp, kW, PS and BTU/h: what each unit means
The kilowatt is the SI unit and the one regulators use. The others are historical units that are still printed on spec sheets:
- hp (mechanical) = 550 ft·lbf/s = 745.69987 W. US and UK engine ratings (SAE J1349 net hp).
- hp (electric) = exactly 746 W. Used on US electric motor nameplates (NEMA).
- PS / CV (metric hp) = 75 kgf·m/s = 735.49875 W. European and Latin American car specs (German PS, Spanish/Portuguese CV, French ch).
- BTU/h and TR: heating and cooling capacity. 1 TR (ton of refrigeration) = 12,000 BTU/h = 3,516.85 W.
hp to kW and PS conversion table
| hp | kW | PS |
|---|---|---|
| 1 hp | 0.7457 | 1.014 |
| 5 hp | 3.728 | 5.069 |
| 10 hp | 7.457 | 10.14 |
| 25 hp | 18.64 | 25.35 |
| 50 hp | 37.28 | 50.69 |
| 100 hp | 74.57 | 101.4 |
| 150 hp | 111.9 | 152.1 |
| 200 hp | 149.1 | 202.8 |
| 300 hp | 223.7 | 304.2 |
| 500 hp | 372.8 | 506.9 |
Worked examples
A European car rated at 150 PS: 150 × 0.73549875 = 110.32 kW, which is 147.9 hp. The metric horsepower is 1.4% smaller than the imperial one, so the PS figure always looks a little higher.
A 24,000 BTU/h mini-split: 24,000 × 0.29307107 W = 7.034 kW of cooling (2 tons). That is the heat it moves, not the electricity it uses: with a typical efficiency (COP around 3) it draws roughly a third of that from the outlet.
Frequently asked questions
How many kW is 1 hp?
1 mechanical horsepower is 0.7457 kW (745.7 W). An electric motor horsepower is exactly 746 W, and a metric horsepower (PS/CV) is 0.7355 kW.
Is PS the same as hp?
No. 1 PS (metric horsepower) is 735.5 W and 1 hp is 745.7 W, so 100 PS = 98.6 hp. The difference is about 1.4%.
How many kW is a 12,000 BTU air conditioner?
12,000 BTU/h is 3.517 kW of cooling (1 ton). It usually draws only about 1–1.3 kW of electricity, because it moves heat rather than making it.