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Horsepower from Torque Calculator

Convert torque and RPM into horsepower.

How it is calculated

The tool uses the standard relation hp = torque × rpm / 5252, where torque is in pound-feet (lb-ft) and rpm is engine speed in revolutions per minute. The constant 5252 comes from converting the unit of power (one horsepower = 33,000 ft-lb per minute) and 2π radians per revolution. It then converts to kilowatts with kW = hp × 0.745699872 (mechanical horsepower).

RPM must be zero or more. If your torque is in newton-metres, multiply by 0.73756 first to get lb-ft. The result is the power at that single rpm only, because torque and power both change across the rev range. It is crankshaft power from your input, not what reaches the wheels after drivetrain loss.

Worked example

An engine makes 300 lb-ft at 5,000 rpm. hp = 300 × 5,000 / 5252 = 1,500,000 / 5252 = 285.61 hp. In kilowatts, 285.61 × 0.745699872 = 212.98 kW.

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Common mistakes

  • Entering torque in N·m without converting it to lb-ft, which understates horsepower by about 26%.
  • Using the peak torque with the peak-power rpm. The two peaks happen at different speeds, so match the torque to the rpm where it was measured.
  • Expecting the result to be wheel horsepower. Gearbox, differential and tyre losses make wheel power lower.
  • Mixing metric horsepower (PS) with mechanical horsepower (hp). The tool gives mechanical hp; PS is about 1.4% smaller.

About this calculator

This calculator converts engine torque and rotational speed into horsepower using the standard formula HP = (Torque in lb-ft × RPM) / 5252, a relationship derived from the definition of power as the rate of doing rotational work (P = τω) with the units folded into that constant 5252. It also gives the equivalent in kilowatts using P(kW) = τ(N·m) × RPM / 9549 (or via 1 hp ≈ 0.7457 kW).

Automotive engineers, tuners, and gearheads use this to convert dynamometer torque readings into the horsepower figures used in marketing and comparisons, and it's why, when torque is plotted in lb-ft and power in hp, the two curves always cross at exactly 5252 RPM on a dyno chart.

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