Horsepower Calculator
Convert torque and RPM into crank, wheel, and corrected horsepower with optional ET-based estimates.
Power Inputs
Results
Corrected: 0 hp
What is a Horsepower Calculator?
The Horsepower Calculator turns torque, RPM, vehicle weight, and quarter-mile ET into horsepower estimates. It also accounts for drivetrain losses and altitude so you can compare crank vs wheel horsepower with realistic correction factors.
Use it before dyno sessions, bench racing conversations, or parts purchases to know how much power you are really making or need to hit your goals.
Feed it measurements from the Compression Ratio Calculator, confirm delivery in the Fuel Pump Calculator, monitor efficiency with the BSFC Calculator, and budget track fuel via the Gas Calculator.
Best for:
- Engine swaps - Validate whether a new powerplant meets the target wheel horsepower and fuel requirements.
- Dyno comparisons - Normalize different dyno results by applying the same drivetrain loss and altitude factors.
- Drag racing - Estimate horsepower using trap speed or elapsed time before investing in dyno time.
- Towing & load planning - Compare power-to-weight ratios for heavy duty trucks or tow rigs.
How the Horsepower Calculator Works
Horsepower from torque uses the classic formula HP = Torque × RPM ÷ 5252. Wheel horsepower subtracts drivetrain losses set by you.
Altitude correction uses the standard pressure at sea level (14.696 psi) and scales horsepower by the ratio of sea-level pressure to local pressure. Optional weight/ET calculation uses the empirical formula from drag racing.
- Torque units convert between lb-ft and N·m automatically.
- Local pressure is derived from altitude assuming ISA conditions.
- Power-to-weight uses wheel horsepower per 1,000 lb for easy comparisons.
Key Concepts Explained
Torque vs horsepower
Torque measures twisting force while horsepower measures how quickly that torque is delivered.
Drivetrain loss
Automatic transmissions, big tires, and heavy gear oil increase losses; lighter drivetrains lose less power.
Altitude density
Each 1,000 ft of elevation costs roughly 3% of naturally aspirated power without forced induction.
Power-to-weight ratio
Comparing HP per 1,000 lb highlights how quickly a vehicle accelerates regardless of its absolute power.
How to Use This Calculator
Enter torque & RPM
Use dyno sheets or manufacturer specs for torque and peak RPM.
Set drivetrain loss & altitude
Use typical losses (15% manual, 18% automatic) and the altitude where you drive.
Add weight & ET (optional)
Enter quarter-mile elapsed time and race weight to compare against dyno-based estimates.
Review outputs
Compare crank, wheel, corrected horsepower, kilowatts, and power-to-weight in one view.
Benefits of Using This Horsepower Calculator
- • Unified data – Compare builds using consistent assumptions without spreadsheet work.
- • Budget planning – Know if you need bigger injectors, fuel pumps, or cooling before spending money.
- • Performance targets – Translate drag-strip goals into the horsepower required to hit them.
- • Education – Visualize the relationship between torque, RPM, and horsepower instantly.
Factors That Affect Your Results
- • Instrumentation – Uncalibrated dynos or inaccurate torque data change everything.
- • Weather – Humidity and barometric pressure also affect density beyond altitude.
- • Tire & drivetrain setup – Larger tires and heavy fluids raise drivetrain loss.
- • Driver technique – ET-based horsepower assumes optimal launch and shift points.
Frequently Asked Questions
How do I calculate horsepower from torque?
Horsepower equals torque (lb-ft) multiplied by RPM and divided by 5252. The calculator also accepts Newton-meters and converts to lb-ft automatically.
What does drivetrain loss represent?
Drivetrain loss is the percentage of power consumed by the transmission, differential, and tires. Subtracting it from crank horsepower gives wheel horsepower.
Why adjust horsepower for altitude?
Air density drops with altitude, reducing engine output. The calculator uses the standard atmosphere formula to correct power back to sea-level conditions.
Can I estimate horsepower using quarter-mile elapsed time?
Yes. Enter vehicle weight and quarter-mile ET to see an estimated crank horsepower using the common drag-racing formula HP = Weight ÷ (ET ÷ 5.825)3.
How accurate are these numbers?
They provide solid estimates for comparison and planning. For precise values use a calibrated engine or chassis dynamometer.