HP & Torque Lab
Convert between horsepower, torque, and RPM — and plot a simple power curve.
How to Use
- Enter your engine's peak torque and the RPM it occurs at, plus the redline.
- The lab models torque and horsepower curves across the whole rev range.
- Read peak HP and the RPM it lands at, and see where the curves cross at 5252.
- Just need a quick HP = (torque × RPM) / 5252 figure? Use the Horsepower Calculator.
Show Work
Formulas
History of Horsepower
James Watt coined "horsepower" in 1782 to market his steam engines against the draft horses they replaced. He measured a typical brewery horse lifting 33,000 foot-pounds of load per minute — rounding generously, since actual average horses manage closer to 22,000 ft-lb/min over an 8-hour shift. The 33,000 ft-lb/min figure became the imperial mechanical horsepower standard still used today (550 ft-lb/s).
The famous "5252 constant" in HP = (torque × RPM)/5252 falls out of the unit conversion: 33,000 ft-lb/min ÷ 2π radians/rev = 5252.1 ft-lb/rev. Its practical consequence: on any dyno graph, the HP and torque curves always cross at exactly 5252 RPM, because that's the RPM at which 1 lb-ft = 1 HP. This single constant is the reason HP overtakes torque past 5252 RPM for engines that keep breathing.
Metric horsepower (PS in Germany, CV in France/Spain, pk in the Netherlands) is slightly different: 75 kg-m/s = 735.5 W, versus imperial 745.7 W. A "300 PS" BMW and a "300 HP" Ford differ by about 1.4%. Modern automakers often quote both or state compliance with the SAE J1349 "certified net" measurement standard, which specifies atmospheric corrections, accessory loads, and fuel grade.
About This Calculator
Enter any two of horsepower, torque (lb-ft), and RPM; the third computes automatically via HP = (torque × RPM) / 5252. Metric equivalents (Nm, kW, PS) are shown in parallel. At 5252 RPM, HP numerically equals torque — the crossover point that every dyno chart illustrates.
Remember this is engine crank power. Wheel HP from a chassis dyno is typically 10-20% lower due to drivetrain losses (manual transmissions lose ~15%, autos ~20-25%, AWD systems higher). For honest drag-strip predictions, use wheel HP and add a driver-reaction time estimate. Everything runs client-side; no values leave your browser.
About the HP & Torque Lab
Use the HP & Torque Lab — a free, easy tool for automotive and vehicle projects. Nothing is uploaded, and you do not need an account. Convert between horsepower, torque, and RPM — and plot a simple power curve.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Why 5252?
The constant that converts lb-ft and RPM into horsepower: 33,000 ft-lb/min per HP ÷ 2π.
Metric?
Toggle units — Nm and kW are computed in parallel.
How do I use the HP & Torque Lab?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Dyno sanity check
Cross-check a shop dyno sheet.
Gearing decisions
See where peak power lands vs redline.
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