Horsepower Unit Converter
Convert between every type of horsepower: Mechanical, Metric (PS), Electric, Boiler, and Water HP — with a full conversion table at any value.
All Conversions at Your Input Value
Enter any value above and the table below updates automatically.
| Unit | Symbol | Value | Watts Equivalent |
|---|
Horsepower Unit Conversion Factors
Metric HP (PS) = 735.499 W
Electric HP = 746.000 W
Boiler HP = 9,809.500 W
Water HP = 746.043 W
The different horsepower definitions arise from historical context. Mechanical horsepower was coined by James Watt and defined as 550 ft·lbf/s — the rate at which one draft horse could work continuously. This equals 745.699 watts.
Metric horsepower (PS, from German Pferdestärke or French cheval-vapeur / CV) was defined metrically as 75 kgf·m/s = 735.499 watts. This is the unit commonly reported for European vehicles. A 300 PS BMW is approximately 296 mechanical HP.
Electric horsepower is exactly 746 W by definition, making it fractionally larger than mechanical HP. The difference is only 0.04% and is negligible for everyday use.
Boiler horsepower is by far the largest unit — one boiler HP equals 9,809.5 watts or about 13.155 mechanical HP. It measures the rate of heat output from steam boilers and is completely unrelated to engine power.
Worked Example
Vehicle manufacturers may round HP figures or use different measurement conditions (SAE net vs gross, DIN standards). Always verify against official manufacturer documentation for precise comparisons.
Frequently Asked Questions
Mechanical horsepower (hp) = 745.7 watts, defined in the imperial system. Metric horsepower (PS/CV) = 735.5 watts, defined in the metric system. The difference is about 1.4%, meaning a 300 PS European car makes roughly 295.9 mechanical HP. When comparing a European spec sheet to a US EPA rating, always check which unit was used.
Boiler horsepower (BHP) measures the output of steam boilers — defined as the heat needed to evaporate 34.5 lb of water per hour at 212°F (100°C). One boiler HP = approximately 9,810 watts or 13.155 mechanical HP. It is completely unrelated to vehicle engine power and is used exclusively in industrial heating applications.
Electric horsepower is defined as exactly 746 watts. It is used for electric motor ratings by the National Electrical Manufacturers Association (NEMA). The difference from mechanical HP (745.7 W) is only 0.04%, so the two are interchangeable for most practical purposes.
Multiply mechanical HP by 0.7457 to get kilowatts. For example, 400 HP × 0.7457 = 298.3 kW. To convert kW back to HP, multiply by 1.3410. For metric PS, multiply by 0.7355 (PS to kW) or 1.3596 (kW to PS). Use our HP to kW calculator for quick conversions.
Mechanical (imperial) HP, metric HP (PS), electrical HP, boiler HP, and hydraulic HP. They differ slightly: 1 mechanical HP = 745.7 W while 1 metric PS = 735.5 W.