To convert kilowatts to mechanical horsepower, multiply kW by approximately 1.34102. To convert kilowatts to metric horsepower, often written PS, multiply by approximately 1.35962. For example, 10 kW is about 13.41 mechanical hp or 13.60 PS. Both answers describe the same power using different units.
The important first step is choosing the horsepower convention. A calculator that silently assumes mechanical horsepower can disagree with a specification using metric horsepower even when both calculations are correct. Keep the convention beside the answer instead of writing an unexplained “hp.”
Which horsepower unit are you converting?
Mechanical horsepower is defined as 550 foot-pounds-force per second and is approximately 745.6999 watts. Metric horsepower is approximately 735.4988 watts. NIST’s conversion table lists these separately, along with other specialized horsepower units. This guide uses the mechanical and metric conventions throughout.
PS stands for Pferdestärke and denotes metric horsepower in the usage discussed here. Volkswagen’s technical specification notes explicitly identify PS as metric horsepower. Do not assume every document using the English word horsepower has already made that distinction.
A metric horsepower is slightly smaller than a mechanical horsepower, so the same power has a slightly larger numerical value in PS. The difference is about 1.39 percent when comparing the numerical PS value with the mechanical-hp value for the same power. That difference comes from unit definitions, not a change in the underlying power.
Convert kilowatts to horsepower step by step
For mechanical horsepower, divide the kilowatt value by 0.7456999. For metric horsepower, divide by 0.7354988. These denominators are the rounded watt conversion factors above divided by 1,000. The convenient multipliers 1.34102 and 1.35962 are their approximate reciprocals.
Suppose an abstract power value is 7.5 kW. In mechanical horsepower, 7.5 ÷ 0.7456999 = 10.057665…, which rounds to 10.06 mechanical hp. With the metric convention, 7.5 ÷ 0.7354988 = 10.197161…, or 10.20 PS. Choose one convention for the answer or label both clearly.
A second example is 25 kW: 25 ÷ 0.7456999 gives about 33.53 mechanical hp, while 25 ÷ 0.7354988 gives about 33.99 PS. There is no additional time factor in either calculation because both sides are units of power.
Work backward from horsepower to kilowatts
Reverse the calculation by multiplying rather than dividing. Mechanical hp × 0.7456999 gives kW; metric horsepower or PS × 0.7354988 gives kW. Use the same convention in both directions so a round-trip check actually tests your arithmetic.
For example, 20 mechanical hp is approximately 20 × 0.7456999 = 14.913998 kW, normally written 14.91 kW. By comparison, 20 PS is approximately 20 × 0.7354988 = 14.709976 kW, or 14.71 kW. Equal horsepower numbers under different conventions do not represent equal power.
To convert directly between the two conventions, pass through kilowatts. Ten mechanical hp becomes approximately 7.456999 kW, then 7.456999 ÷ 0.7354988 = 10.138696… PS. In the opposite direction, 10 PS becomes about 9.86 mechanical hp. Keeping the intermediate value avoids compounding rounded shortcuts.
Where watts fit into the calculation
The prefix kilo means 1,000: one kilowatt is 1,000 watts. Start with watts by dividing by 1,000 to obtain kilowatts, then apply the chosen horsepower conversion. Alternatively, divide watts directly by 745.6999 for mechanical hp or by 735.4988 for metric horsepower.
For a given 2,000 W value, the first route is 2,000 ÷ 1,000 = 2 kW. That equals about 2.68 mechanical hp or 2.72 PS. Dividing 2,000 directly by the matching watt-per-horsepower factor produces the same answer. This is a useful check for accidentally losing a factor of 1,000.
Power, energy and torque need different information
NIST defines a watt as a unit of power equal to one joule per second. Power describes a rate of energy transfer. Energy describes an accumulated amount. A kilowatt-hour therefore cannot be converted directly to horsepower without information about the time involved.
For instance, 6 kWh transferred over 3 hours corresponds to an average power of 2 kW, or about 2.68 mechanical hp. The same 6 kWh over 6 hours corresponds to 1 kW, or about 1.34 mechanical hp. These averages do not describe every instant. Our kilowatt-hour guide explains the energy-and-time calculation in more detail.
Torque is a turning effect, commonly expressed in newton-metres. Rotational power depends on both torque and angular speed, as described in Nidec’s explanation of power and torque. A torque figure alone does not determine horsepower, and changing a power unit does not supply a missing speed.
Electrical input and mechanical output are separate quantities
Kilowatts can describe electrical input or mechanical output, depending on what was measured or specified. Converting the unit preserves that meaning. A number stated as electrical input does not become mechanical output simply because it is expressed in mechanical-horsepower units.
Nidec’s motor basics distinguishes electrical input from mechanical output and defines efficiency through their ratio. You need that additional relationship to move between input and output. A unit conversion alone makes no claim about efficiency, performance or suitability.
A final check before copying your answer
Record the original number, whether it describes input or output, and the horsepower convention. Keep extra calculator digits until the final step, then round to a precision appropriate to the starting value. Our rounding and precision guide explains why more displayed decimal places do not make a measurement more accurate.
For positive values, remember the direction: kilowatts to either horsepower convention increases the numerical value; horsepower to kilowatts decreases it. This quick check catches many reversed operations. It does not replace checking the original unit label.
For paper calculations, you can browse graph-paper notebooks on Amazon.
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