Horsepower vs kW vs PS — What's the Difference?

Where Each Unit Comes From

Horsepower was defined by James Watt in the 1780s to help sell steam engines. Watt needed to convince customers that his engines could replace horses — so he measured how much work a horse could do and defined 1 hp as 33,000 foot-pounds of work per minute. This is still the definition of mechanical (or imperial) horsepower today.

The metric equivalent — PS (Pferdestärke, German for "horsepower") — was standardized later using metric units: 1 PS = the power needed to lift 75 kilograms by 1 meter in 1 second = 735.499 watts. Because PS is defined with slightly different round numbers, 1 PS = 0.98632 hp. The two are close enough that they are often used interchangeably, but performance car buyers notice the difference.

Kilowatts are simply SI units applied to power. 1 kW = 1,000 joules per second. The European Union mandated kW as the primary power unit for cars in 1992, which is why every European car spec sheet lists power in kW (with hp or PS in parentheses).

Conversion Factors

1 hp (mechanical) = 745.7 W = 0.7457 kW = 1.0139 PS.

1 PS = 735.5 W = 0.7355 kW = 0.9863 hp.

1 kW = 1,000 W = 1.341 hp = 1.360 PS.

For quick mental math: hp × 0.75 ≈ kW. kW × 1.34 ≈ hp. The error is under 1% using these rounded factors.

Real Cars: Power in Three Units

A few reference cars show how the numbers look across all three units.

Why Electric Cars Use kW

Electric motors are rated in kW because it is the natural electrical unit — power in an electrical circuit equals voltage times current, both of which are measured in SI units. Converting to hp is possible but adds no technical value; the hp unit was invented for combustion engines and horses, not electrons.

Tesla lists the Model 3 Performance at 358 kW (480 hp equivalent). Rivian's R1T truck peaks at 522 kW (700 hp). The shift to EV specs published primarily in kW is gradually making European car buyers more comfortable with the unit — which was the EU's intent when it mandated kW in 1992.

For consumers comparing a gasoline car to an EV: multiply the EV's kW rating by 1.34 to get the hp equivalent. 150 kW EV = 201 hp equivalent. This is a rough comparison — electric motors deliver peak torque instantly from 0 rpm, which makes the same kW feel more powerful off the line than a combustion engine with the same peak rating.

Conclusion

hp, PS, and kW all measure the same thing — engine output — with slightly different origins and scale factors. 1 hp = 0.7457 kW = 1.014 PS. For everyday comparison, use hp × 0.75 ≈ kW and kW × 1.34 ≈ hp. Electric car specs increasingly appear in kW, making fluency in both units increasingly useful.