Torque from Horsepower Calculator
Work out engine torque in lb-ft from horsepower and RPM using torque = hp × 5252 ÷ RPM.
How it works
Torque (lb-ft) = horsepower × 5252 ÷ RPM
This is the horsepower equation rearranged to solve for torque. Since horsepower is torque times RPM divided by 5,252, multiplying power by 5,252 and dividing by the engine speed returns the torque. The practical takeaway is that peak power at a low RPM implies big torque, which is why diesels and large-displacement engines that make their horsepower down low feel so strong from a standstill.
Worked example
An engine rated 300 hp at 5,252 RPM is making exactly 300 lb-ft (about 406.7 Nm). If it instead hit that same 300 hp at only 3,500 RPM, the torque would be 300 × 5,252 ÷ 3,500 ≈ 450 lb-ft.
Frequently asked questions
Why does the same horsepower give more torque at lower RPM?
Torque is horsepower divided by engine speed (times 5,252). If an engine makes its rated power at a lower RPM, each revolution must carry more twisting force, so the torque figure is higher.
What RPM should I use — peak power RPM?
To find peak torque you would need the RPM at peak torque, not peak power. Plugging in the peak-power RPM gives the torque at that specific point, which is usually below the engine’s maximum torque.
How do I convert lb-ft to Nm?
Multiply pound-feet by 1.35582. So 300 lb-ft is about 406.7 Nm. Newton-metres are the metric torque unit used on most non-US spec sheets.
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Educational estimate. Real-world results vary with conditions, tuning and measurement.