Engine Horsepower Calculator
Estimate engine horsepower from a quarter-mile run. Choose trap speed or elapsed time, enter the vehicle weight, and get an approximate power figure.
Quarter-mile data
This is an estimate based on power-to-weight, closer to power at the wheels than the crank (flywheel) figure manufacturers quote. Real results depend on traction, aerodynamics, gearing, and air conditions.
How to use this calculator
1. Choose a method
Pick trap speed if you know the mph at the end of the quarter mile, or elapsed time (ET) if you only have the run time. Each uses a different empirical equation.
2. Enter the vehicle weight
Use the full race weight including the driver and any fuel. Weight has a strong effect on the estimate, so be as accurate as you can.
3. Enter your run figure
Add the trap speed in mph or the elapsed time in seconds. The result updates instantly as you type.
4. Read the estimate
The big number is the estimated horsepower. Treat it as a ballpark — it reflects real-world losses, not a controlled dyno run.
About horsepower estimates
The trap-speed equation
HP = weight × (mph ÷ 234)³. Known as the Hale formula, it links the speed a car reaches over a fixed distance to its power-to-weight ratio. Our default 3000 lb at 100 mph estimates about 234 HP.
The elapsed-time equation
HP = weight ÷ (ET ÷ 5.825)³. This Fox formula derives power from the quarter-mile time alone, so it is handy when no trap-speed reading was captured.
Wheel vs. crank power
These methods estimate power roughly at the wheels and include drivetrain and aerodynamic losses. Manufacturer crank ratings are higher because they are measured at the flywheel, so don't expect an exact match.