Horsepower Calculator
Convert torque and RPM into horsepower, or work backwards.
How this calculator works
HP = torque (lb-ft) × RPM ÷ 5252
The constant 5252 is where the horsepower and torque curves always cross on a dyno chart — it comes from 33,000 ft-lb per minute divided by 2π. If your curves cross anywhere else, the plot is wrong.
Switch the site to metric — the control is in the footer — and your inputs, your results and the tables below follow. The formula, the constants, the guidance text and the sources stay in US units on purpose: that is how the standards they come from are written, and restating them would detach each figure from the document you are meant to be able to check it against.
Where these numbers come from
- NIST Special Publication 811 2008 — mechanical horsepower as 33,000 ft·lbf per minute, from which the 5252 constant follows as 33,000 ÷ 2π
Cited to a specific edition on purpose — table numbers and values move between cycles. Confirm against whichever edition is enforced locally.
Worked example
With torque 300 , engine speed 5000 , this calculator returns 285.61 .
Horsepower at common torque and RPM figures
Each row is a link that fills in the calculator above. Send one and the other end sees the same figures you do.
| Job | Size | Horsepower |
|---|---|---|
| Diesel pickup, peak torque | 900 × 1800 | 308.5 |
| Naturally aspirated V8 | 400 × 4500 | 342.7 |
| Small four-cylinder | 150 × 6000 | 171.4 |
| Motorcycle twin | 80 × 7000 | 106.6 |
| At the 5252 crossover Horsepower equals torque here, always |
300 × 5252 | 300.0 |
Frequently asked questions
What is the difference between torque and horsepower?
Torque is rotational force; horsepower is the rate at which that force does work. Torque tells you how hard the engine pulls, horsepower how fast it can keep doing it.
Why do torque and horsepower cross at 5252 RPM?
It falls out of the formula. Horsepower is torque times RPM divided by 5252, so at exactly 5252 RPM the two are numerically equal. Every correct dyno chart shows the curves crossing there.
How do I convert horsepower to kilowatts?
Multiply by 0.7457. Three hundred horsepower is about 224 kW. Metric horsepower, used in European specifications, is slightly different at 0.7355 kW.
Does more torque mean faster acceleration?
At the wheels, yes — but gearing multiplies torque, so a high-revving engine with modest torque can out-accelerate a low-revving one. What matters is area under the power curve across the usable rev range.