What Is HP to Torque Conversion?
A dyno chart shows two curves — horsepower and torque — plotted against RPM, and students learning engine fundamentals often assume they're separate measurements. They're not. Torque and horsepower are mathematically locked together by RPM: once you know any two of the three numbers, the third is fixed. This calculator solves for torque when you already know the horsepower and the engine speed.
Understanding the conversion matters because torque is what you feel — it's the twisting force at the crankshaft that accelerates the car — while horsepower is a calculated rate of doing work over time. Reading both correctly is essential to comparing engines fairly.
The HP to Torque Formula
[
\text{Torque (lb-ft)} = \frac{\text{Horsepower} \times 5252}{\text{RPM}}
]
The constant 5252 comes from the definition of horsepower itself: one horsepower equals 33,000 ft-lb of work per minute, and dividing that by 2π (the number of radians in a full revolution) gives 5252.11, conventionally rounded to 5252. It is a fixed conversion factor, not something you adjust per engine.
To convert the result to Newton-meters, multiply by 1.35582, the standard lb-ft-to-N·m conversion:
[
\text{Torque (N·m)} = \text{Torque (lb-ft)} \times 1.35582
]
Worked Example
Say an engine is rated at 300 horsepower and you want to know the torque it produces at 6000 RPM:
[
\text{Torque (lb-ft)} = \frac{300 \times 5252}{6000} = \frac{1{,}575{,}600}{6000} = 262.60 \text{ lb-ft}
]
Converting that to metric units:
[
\text{Torque (N·m)} = 262.60 \times 1.35582 = 356.04 \text{ N·m}
]
So a 300 HP engine turning 6000 RPM is putting out about 262.6 lb-ft (356.0 N·m) of torque at that instant. Plug the same numbers into the calculator above and you'll get an identical result.
The Crossover Point at 5252 RPM
One quirk of the formula catches a lot of students by surprise: whenever RPM equals exactly 5252, horsepower and torque are numerically equal, regardless of the engine.
[
\text{Torque} = \frac{250 \times 5252}{5252} = 250 \text{ lb-ft} = 250 \text{ HP at that RPM}
]
That's not a design coincidence — it falls straight out of the algebra. It's also why, on a dyno graph, the torque and horsepower curves always cross at the 5252 RPM mark: below that speed torque reads higher than horsepower, and above it horsepower reads higher.
Torque vs Horsepower at a Glance
| RPM relative to 5252 | Torque curve | Horsepower curve |
|---|---|---|
| Below 5252 | Reads higher | Reads lower |
| At 5252 | Equal | Equal |
| Above 5252 | Reads lower | Reads higher |
This is why a diesel truck engine, which rarely spins past 3000-4000 RPM, is described in terms of torque, while a high-revving sport-bike engine spinning to 12,000+ RPM is described in terms of horsepower — each is simply reporting the number that looks bigger at its normal operating range.
Quick Recap
- T = HP × 5252 ÷ RPM gives torque in lb-ft; multiply by 1.35582 to get N·m.
- 5252 is a fixed constant from horsepower's definition, not a variable.
- Horsepower and torque are always numerically equal at 5252 RPM.
- Use the calculator above to convert any horsepower-and-RPM pair into a torque figure in either unit.
If you're working through engine output figures, the RPM to torque calculator is a useful companion for the reverse direction.