Horsepower Calculator
Calculate horsepower from torque and engine speed, or compare imperial and metric torque values instantly.
Enter peak torque measured on a dyno or provided by the manufacturer.
How to Use This Calculator
Enter engine torque
Select lb-ft or N·m and input torque measured at the crank or wheels.
Add engine RPM
Use the RPM at which the torque was measured, often the point of peak power.
Calculate horsepower
Press calculate to convert torque and RPM into horsepower and kilowatts instantly.
Interpret the results
Compare output to manufacturer specs or dyno charts, and convert between HP and kW.
Formula
Horsepower = (Torque × RPM) ÷ 5252
This constant (5252) converts lb-ft and RPM into horsepower. For metric torque, we convert N·m to lb-ft before applying the formula.
Example: 320 lb-ft at 5,200 RPM → HP = (320 × 5200) ÷ 5252 = 317.1 hp
Kilowatts = Horsepower × 0.7457 → 317.1 hp × 0.7457 = 236.6 kW
About the Horsepower Calculator
Horsepower expresses how quickly work can be performed. Whether you're tuning a car, sizing industrial motors, or comparing motorcycles, this calculator turns torque and engine speed into real power output.
When to Use This Calculator
- Dyno analysis: Convert torque curves into horsepower graphs.
- Performance upgrades: Estimate gains after cams, turbos, or exhaust mods.
- Motor sizing: Match industrial motors or generators to load requirements.
- Educational demos: Illustrate the relationship between torque, RPM, and power.
Why Use Our Calculator?
- ✅ Metric + Imperial: Converts torque between lb-ft and N·m on the fly.
- ✅ Accurate constants: Uses precise conversion factors for professional results.
- ✅ Instant kilowatts: View output in metric units without extra steps.
- ✅ Mobile-ready: Use it trackside, in the shop, or during classroom labs.
Common Applications
Automotive tuning: Analyze dyno pulls or simulation outputs.
Motorcycle performance: Convert factory torque specs to horsepower.
Industrial engineering: Size electric motors for pumps, compressors, and conveyors.
Tips for Best Results
- Use wheel torque for wheel horsepower and crank torque for crank horsepower.
- Measure torque at the RPM where you want horsepower; peak torque doesn't always equal peak horsepower.
- Consider drivetrain losses (10–20%) when comparing crank and wheel numbers.
- Combine this tool with acceleration or trap-speed calculators for a full performance picture.
Frequently Asked Questions
Why is 5,252 used in the formula?
The constant 5,252 derives from unit conversions between torque (lb-ft), rotational speed (RPM), and horsepower. It equals 33,000 ÷ 2π and ensures consistent imperial units.
What's the difference between horsepower and kilowatts?
Both measure power. One mechanical horsepower equals 0.7457 kilowatts. Many countries use kW in vehicle specs, while hp is still common in the U.S.
How accurate is horsepower from torque?
The calculation is exact if torque and RPM are accurate. Differences arise from measurement errors, drivetrain losses, or using wheel torque for crank horsepower.
Can I reverse the formula to get torque?
Yes. Torque (lb-ft) = Horsepower × 5,252 ÷ RPM. Our results section provides both torque units for quick reference.