American and European horsepower usually differ because they use different units, not because the engine itself changed. In the common comparison, American “hp” means mechanical horsepower and European “PS” means metric horsepower. One mechanical hp is about 1.014 PS, so 200 PS converts to roughly 197 mechanical hp. The kilowatt (kW) is the clearest unit for comparing the two.
What is the difference between American hp and European PS?
Mechanical horsepower and metric horsepower are close, but they are not identical. The U.S. Bureau of Standards’ 1915 circular defined English horsepower as 550 foot-pounds per second, or 746 watts, and continental horsepower as 75 kilogram-meters per second, or 736 watts. Those rounded watt equivalents make mechanical horsepower about 1.4% larger than PS.
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“European horsepower” is informal shorthand, not a single rule for every European country or carmaker. PS comes from the German word Pferdestärke, meaning horsepower. A maker may publish power in PS, hp, or kW; check the unit shown rather than inferring it from where the vehicle is sold.
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How to convert PS, hp and kW
| Conversion | Multiply by | Basis |
|---|---|---|
| Mechanical hp to kW | 0.7457 | Standard mechanical-horsepower conversion stated in a 2010 NHTSA-hosted Federal Register proposal: Federal Register PDF. |
| PS to kW | Approximately 0.7355 | Metric horsepower definition; the Bureau’s 1915 circular rounds this to 736 W. |
| PS to mechanical hp | Approximately 0.986 | Calculated from the Bureau’s rounded watt equivalents. |
| Mechanical hp to PS | Approximately 1.014 | Calculated from the Bureau’s rounded watt equivalents. |
For example, 200 PS × 0.7355 = 147.1 kW; 147.1 ÷ 0.7457 = about 197.3 mechanical hp. Answers can vary slightly with rounding.
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The Bureau’s 1915 circular recommended using watts and kilowatts where possible, noting that practice was tending toward wider use of the kilowatt and away from horsepower. That makes kW a useful common ground when a specification sheet uses PS and another uses hp. U.S. Bureau of Standards Circular 34, third edition.
Why a unit conversion does not settle an engine comparison
Converting the unit only puts the stated number on the same scale. It does not establish that two engines were rated under the same test procedure or on the same basis. SAE J2723 specifies how manufacturers certify production-engine net power and torque ratings under SAE J1349, or gross engine power under SAE J1995. SAE says certification is voluntary, but its certification process is mandatory for manufacturers advertising ratings as certified to either standard. SAE J2723_202110.
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If two figures differ by more than the roughly 1.4% unit gap, do not attribute the entire difference to American versus European horsepower. Compare the exact model, engine and market version, along with the stated test or certification basis. Also check whether the figure is engine output or a different measurement, such as power at the wheels. Without those details, a converted number is not a like-for-like vehicle comparison.
What to check on a vehicle specification sheet
- Unit: Is the figure in hp, PS or kW?
- Exact vehicle: Does it refer to the same model, engine and market version?
- Rating basis: Is a test or certification standard stated?
- Measurement location: Is it engine output or wheel power?
The Bureau’s 1915 circular described continental horsepower as used in Germany and France and generally on the continent at that time. That is historical context, not proof of present-day labeling rules in every European country. The unit definitions explain the conversion; vehicle- and jurisdiction-specific details require checking the applicable specification or rule.
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