Torque from Horsepower Calculator
Calculate engine torque in lb·ft from horsepower and RPM using Torque = HP × 5252 ÷ RPM.
How to use this tool
- Enter the horsepower rating from the spec sheet or dyno.
- Enter the RPM at which that power is produced.
- The result is torque in pound-feet using the formula Torque = HP × 5,252 ÷ RPM.
Find engine torque from a known horsepower figure and RPM.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
Torque (lb·ft) = HP × 5252 ÷ RPM
The constant 5252 comes from converting horsepower to foot-pounds per minute: 1 HP = 33,000 ft·lbf/min, and 33,000 ÷ (2π) ≈ 5252.
How it works
This calculator converts engine power (horsepower) to torque at a given engine speed using the fundamental rotational mechanics relationship between power, torque, and angular velocity. It assumes steady-state power delivery at the specified RPM — real-world torque curves vary across the RPM band. The result is the theoretical output torque at the crankshaft before drivetrain losses.
Worked example
- Input: 300 HP at 5252 RPM.
- Apply the formula: Torque = 300 × 5252 ÷ 5252.
- The 5252 terms cancel: Torque = 300 × 1 = 300 lb·ft.
- Note: horsepower and torque curves always cross at exactly 5252 RPM.
Torque = 300.0 lb·ft
Common mistakes to avoid
- Plugging in rated HP at an RPM different from where that HP is produced, giving a torque figure that does not match the actual engine curve at that speed.
- Using wheel horsepower with flywheel RPM -- wheel HP is already reduced by drivetrain losses, so the resulting torque understates crank torque.
- Forgetting that 5,252 RPM is where HP and lb-ft are numerically equal; applying the formula at idle RPM produces implausibly large torque numbers.
Key terms
- Horsepower (HP)
- A unit of power equal to 550 foot-pounds of work per second or 33,000 foot-pounds per minute, commonly used to rate engine output.
- Torque (lb·ft)
- A rotational force measured in pound-feet; it describes how much twisting force an engine produces at the crankshaft.
- RPM
- Revolutions per minute — the rate at which the engine crankshaft completes full rotations.
- 5252 constant
- Derived from 33,000 ÷ (2π), it is the RPM value at which an engine's horsepower and torque curves always intersect numerically.
Frequently asked questions
- How do I calculate torque from horsepower?
- Use Torque (lb·ft) = HP × 5,252 ÷ RPM. For example, 400 HP at 6,000 RPM produces 400 × 5,252 ÷ 6,000 = 350.1 lb·ft of torque.
- What does higher torque at lower RPM mean?
- High torque at low RPM (common in diesels and turbocharged engines) means the engine feels strong when pulling away from a stop or climbing hills.