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hp to kW converter: power and torque

Convert horsepower, kilowatts and metric horsepower (PS, CV) in one step, switch between N·m and lb-ft, and work out the power an engine makes from its torque and rpm.

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Power converter
Torque converter
Power from torque and rpm

Exact unit conversions. They do not convert between measurement standards (DIN, SAE, ISO, WLTP).

Result

The three kinds of “horsepower”

So 1 hp = 1.0139 PS and 1 kW = 1.3410 hp = 1.3596 PS. The two horsepower units differ by about 1.4 %, which is why the same engine can be listed with slightly different numbers.

Formulas

Power (kW) = torque (N·m) × rpm × 2π / 60 / 1000

Torque (N·m) = lb-ft × 1.35582 (1 lb-ft = 1.3558179 N·m)

Worked example: 400 N·m at 4,000 rpm gives 400 × 4,000 × 2π / 60 = 167,552 W = 167.6 kW = 224.7 hp = 227.8 PS.

Limitations

  • These are exact unit conversions. They do not convert between measurement standards (DIN 70020, SAE J1349, ISO 1585, WLTP…), which can differ by a few percent for the same engine.
  • Power from torque and rpm is the power at that single operating point, read from a torque curve. It is not the engine’s peak power unless you use the peak-power rpm.
  • Wheel power on a dyno is lower than the crankshaft figure because of drivetrain losses, which this tool does not estimate.

Sources

All formulas are covered by automated tests with hand-calculated reference values. Found an error? See the about page. To turn power into speed in each gear, try the gear ratio calculator.

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