Starlight Tools

Horsepower to Torque Calculator

Calculate torque, horsepower, or RPM from the other two values. Convert mechanical hp, metric hp, kW, lb-ft, N·m, and lb-in instantly. Inputs stay in this browser tab.

Use values from the same rotating shaft Power, torque, and RPM must describe the same point and operating condition. Engine-crank and wheel figures differ because gearing and drivetrain losses act between them.

Shaft values

Enter the other two known values.

Use delivered shaft power, not fuel or electrical input.

Revolutions per minute; zero is valid only when calculating power.

Privacy: values are calculated locally. They are not uploaded, stored, or included in analytics events.

Calculated torque

Horsepower, torque, and RPM formulas

Rotational power is torque multiplied by angular speed. In SI units:

power (W) = torque (N·m) × RPM × 2π ÷ 60

For mechanical horsepower and pound-feet, the same relationship becomes:

hp = torque (lb-ft) × RPM ÷ 5,252.113

Rearrange it to find either unknown: torque = hp × 5,252.113 ÷ RPM, or RPM = hp × 5,252.113 ÷ torque. Many references round the constant to 5,252; this calculator uses SI conversions internally for greater precision.

How to use the calculator

  1. Choose the unknown. Select torque, horsepower, or RPM.
  2. Match the source units. Choose mechanical hp, kW, PS, lb-ft, N·m, or lb-in exactly as stated on the source data.
  3. Use one operating point. A peak horsepower value and a peak torque value usually occur at different RPM, so do not combine them unless they describe the same point.
  4. Compare the same shaft location. Do not mix crankshaft power with wheel torque unless losses and gear multiplication have already been accounted for.

Mechanical hp, metric hp, and torque units

  • Mechanical horsepower (hp): 745.6998716 watts. This is the usual horsepower unit in U.S. automotive specifications.
  • Metric horsepower (PS): 735.49875 watts. It is slightly smaller than mechanical horsepower.
  • Kilowatt (kW): 1,000 watts, the SI-compatible power unit commonly used for motors and vehicles.
  • Torque: 1 lb-ft equals 1.355817948 N·m, and 1 lb-ft equals 12 lb-in.

Why 5,252 RPM matters: mechanical hp and lb-ft have the same numerical value at approximately 5,252 RPM. This is a unit-conversion coincidence, not a special engine speed, and it changes when other units are used.

Horsepower and torque FAQs

How do I calculate torque from horsepower and RPM?

Multiply mechanical horsepower by 5,252.113, then divide by RPM to get pound-feet. For example, 300 hp at 6,000 RPM is about 262.61 lb-ft.

How do I calculate horsepower from torque and RPM?

Multiply torque in pound-feet by RPM, then divide by 5,252.113. The torque and speed must apply at the same shaft and operating point.

Why do horsepower and torque cross at 5,252 RPM?

With mechanical hp and lb-ft, the conversion factor makes the numerical values equal at about 5,252 RPM. A graph using kW and N·m will not cross at that RPM.

Is lb-ft the same as ft-lb?

Automotive torque is commonly written lb-ft or ft-lb, but pound-foot of torque is the clearest meaning here. Foot-pound can also describe energy, so context matters.

Are mechanical horsepower and metric horsepower the same?

No. Mechanical hp is about 745.700 W and metric hp (PS) is 735.49875 W. Select the unit actually used by the source specification.

Does this account for drivetrain losses?

No. This calculator applies the rotational relationship at one shaft. It does not estimate transmission, differential, tire, accessory, electrical, or thermal losses.

Can torque exist at zero RPM?

Yes, a shaft can exert static or stall torque at zero speed, but its mechanical power at that instant is zero. The calculator accepts zero when finding power, but requires a positive divisor when solving torque or RPM.

Are my values tracked?

No. The calculation runs locally in your browser and does not upload, store, or attach values to analytics events.

Limits and engineering disclaimer

  • The result is an ideal mathematical conversion. It does not estimate efficiency, heat, traction, acceleration, gearing, or drivetrain loss.
  • Rated, peak, corrected, indicated, brake, crankshaft, PTO, motor-input, and wheel figures are not interchangeable unless they refer to the same measurement boundary.
  • Published dyno and manufacturer values may be rounded or corrected to different atmospheric and test standards.

Engineering disclaimer: Use this result for calculation and comparison, not for component sizing, dyno calibration, safe operating limits, or vehicle modification approval. Follow manufacturer data and qualified engineering guidance for safety-critical work.

Methodology and sources

Last reviewed: July 31, 2026. The relationship and mechanical horsepower conversion were checked against U.S. Department of Energy references:

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