Horsepower Calculator

Horsepower from torque and RPM

• Horsepower = torque (lb·ft) × RPM ÷ 5252 — the classic SAE relationship.
• At 5252 RPM, torque (lb·ft) and horsepower are the same number.
• Toggle lb·ft / N·m and hp / kW to match the units on your dyno sheet or OEM chart.

Torque tells you twisting force; horsepower tells you how fast that work is being done. This free horsepower calculator turns a torque figure and an engine speed into brake power so you can compare cams, estimate a swap, or reverse-check a dyno printout.

Enter torque and the RPM where it was measured. The dyno-cell view shows horsepower with torque and engine speed alongside. Feed crank torque for crank HP, or wheel torque if you want an approximate wheel figure — the math does not invent drivetrain loss for you.

Pair this with the torque calculator when you only have an HP number, and with gear ratio or RPM-at-speed tools when you need to see how that power lands on the road.

Worked examples from the 5252 formula

Same torque at different RPM is different power. A truck that makes 350 lb·ft at 2,400 rpm is not a 350 hp engine — it is about 160 hp at that point. Peak horsepower almost always lives higher in the rev range even if torque has already started to fall.

When this number is the wrong tool

Do not use this page to invent drivetrain loss (a 15% guess is not a measurement), to convert a “up to 400 hp” ad into a dyno sheet, or to size injectors from bumper-sticker power. For injector flow use the injector calculator with a realistic BSFC. For trap speed, use race weight and the power you actually put down — not the SAE peak from a different RPM than you run at the stripe.

How to use the horsepower calculator

1. Enter torque. Use the peak or the RPM point you care about, in lb·ft or N·m.
2. Enter engine RPM. Match the RPM where that torque was measured or estimated.
3. Read horsepower. The dyno cell shows horsepower (and kilowatts) at that operating point.

Horsepower FAQ