Convert kilowatts to mechanical horsepower and metric PS, the two horsepower figures in everyday use.
Sizing the electrical supply for the same machine? Use the kVA to kW calculator.
Every diagram and table on this page updates with the calculator above.
Mechanical horsepower, defined as 745.6999 W.
Metric horsepower, defined as 735.49875 W.
The two definitions differ by about 1.4%, which is why the same engine is quoted slightly differently in different markets. Neither is more correct — they are simply two historical conventions for the same idea.
| Unit | Exact value | Where you meet it |
|---|---|---|
| Mechanical hp | 745.700 W | UK and US vehicles, pumps, compressors |
| Metric hp (PS, CV, pk) | 735.499 W | Continental Europe, Japan, Korea |
| Electrical hp | 746 W exactly | US motor nameplates |
| Boiler hp | 9,809.5 W | Steam boiler ratings — a completely different quantity |
Boiler horsepower is a heat rate, not a mechanical output. Never convert it with the 1.341 factor.
A 100 kW engine is 134 hp or 136 PS. On a brochure that difference is marketing; on a specification it is a discrepancy someone will eventually query.
IEC motors are built to a kilowatt series and NEMA motors to a horsepower series. The two ladders were never aligned, so equivalents are always approximate.
| IEC (kW) | Exact hp | Nearest NEMA (hp) |
|---|---|---|
| 0.75 | 1.01 | 1 |
| 1.5 | 2.01 | 2 |
| 4.0 | 5.36 | 5 |
| 7.5 | 10.06 | 10 |
| 15 | 20.1 | 20 |
| 37 | 49.6 | 50 |
| 75 | 100.6 | 100 |
| 160 | 214.6 | 200 or 250 |
When replacing a motor across the two standards, take the next size up. A 200 hp NEMA motor is slightly smaller than a 160 kW IEC one.
| kW | Mechanical hp (hp) | Metric PS (PS) |
|---|---|---|
| 0.37 kW | 0.5 | 0.5 |
| 0.55 kW | 0.74 | 0.75 |
| 0.75 kW | 1.01 | 1.02 |
| 1.1 kW | 1.48 | 1.5 |
| 1.5 kW | 2.01 | 2.04 |
| 2.2 kW | 2.95 | 2.99 |
| 3 kW | 4.02 | 4.08 |
| 4 kW | 5.36 | 5.44 |
| 5.5 kW | 7.38 | 7.48 |
| 7.5 kW | 10.06 | 10.2 |
| 11 kW | 14.75 | 14.96 |
| 15 kW | 20.12 | 20.39 |
| 18.5 kW | 24.81 | 25.15 |
| 22 kW | 29.5 | 29.91 |
| 30 kW | 40.23 | 40.79 |
| 37 kW | 49.62 | 50.31 |
| 45 kW | 60.35 | 61.18 |
| 55 kW | 73.76 | 74.78 |
| 75 kW | 100.58 | 101.97 |
| 90 kW | 120.69 | 122.37 |
| 110 kW | 147.51 | 149.56 |
| 132 kW | 177.01 | 179.47 |
| 160 kW | 214.56 | 217.54 |
A motor nameplate states mechanical output at the shaft. The electrical input is higher, by the efficiency, and higher again in apparent power terms because of the power factor.
IE3 motors above 10 kW typically reach 92–95% efficiency.
The supply must provide 90.7 kVA to get 75 kW — about 131 A at 400 V three phase.
Fans, pumps and small drives. Often single phase with a start capacitor.
The bulk of industrial motors: conveyors, compressors, process pumps.
Usually medium voltage, with dedicated starting equipment and protection.
A 1.4% discrepancy looks like a measurement error and gets chased for hours.
Boiler hp is 9.81 kW, not 0.746 kW. Converting it as mechanical hp is out by a factor of thirteen.
Nameplate hp is shaft output. The electrical supply must deliver more.
29 calculators built on the same maths as the tool above. Each one has its own inputs, interactive diagrams and worked examples.
Common questions about converting kw to hp.