Horsepower Calculator
Calculate engine horsepower from torque and rpm, and estimate quarter-mile performance.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
Enter torque in lb·ft, engine speed in rpm, vehicle weight in lb and an assumed drivetrain-loss percentage. Horsepower uses the standard torque × rpm ÷ 5,252 relationship. Wheel horsepower and quarter-mile time are simplified estimates, not dyno or track results. Vehicle weight and drivetrain loss are available in advanced options. The engine-power answer remains available without a vehicle-performance estimate.
Worked example
calculated with the default values below
Torque 300 lb-ft · Engine speed 5,000 rpm · Vehicle weight 3,500 lb · Drivetrain loss (assumption) 15 % Horsepower (crank) 285.6 hp · Horsepower at the wheels 242.8 hp · Power 213.0 kW · Power to weight 0.0816 hp/lb · Quarter-mile time (rough estimate) 14.18 s
Method and assumptions
Formula basis and scope
HP_crank = T × rpm ÷ 5252; HP_wheel = HP_crank × (1 − L ÷ 100) P1 consolidation retains the core model and adds input modes or derived outputs. The migration report records the input/output union and known-answer checks.
The references explain definitions and methods; any extra preset must be checked against the assumptions on this page. Added display totals and migration adapters are implementation behavior, not independently validated claims.
Data sources
Disclaimer
These calculators give estimates for general information only. Real fuel consumption, performance and range vary with driving style, load, terrain, temperature and vehicle condition. Do not rely on these results for towing limits, payload or braking decisions — use the rating plate of your vehicle.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
HP = T × RPM ÷ 5252 ; WHP = HP × (1 − D ÷ 100) ; t = 5.825 × (W ÷ WHS)^(1/3)
- T
- torque (lb·ft)
- RPM
- engine speed
- D
- drivetrain loss (%)
- W
- vehicle weight (lb)
- WHS
- wheel horsepower
Kilowatts = HP × 0.7457; power-to-weight = HP ÷ W. Quarter-mile time t in seconds; estimate only.
Frequently asked questions
How is horsepower calculated from torque and rpm?
For torque in lb·ft and engine speed in rpm, crank horsepower = torque × rpm ÷ 5,252. At 5,252 rpm the horsepower and torque numbers are equal, but horsepower is not zero. Wheel horsepower applies the drivetrain-loss percentage you enter; it is an estimate, not a dynamometer measurement.
How should I interpret the quarter-mile time?
It is a rough estimate from vehicle weight and modeled wheel horsepower. It does not account for traction, gearing, aerodynamics, launch, surface or weather, so it is not a track prediction.