Horsepower from Quarter Mile Calculator
Estimate your car’s horsepower from a quarter-mile time slip, or predict ET and trap speed from horsepower.
- HP from ET
- HP from trap speed
- Fox formula
- Pounds per HP
- Eighth mile estimate
- Launch Check
Time Slips
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| Run | Weight | ET | MPH | HP (ET) | HP (MPH) | Remove |
|---|
How to Estimate Horsepower from a Quarter-Mile Run
Drag racers have long used simple power-to-weight formulas to connect horsepower with elapsed time (ET) and trap speed. The best-known are Roger Hale's, which estimate flywheel horsepower:
Older versions use different constants: Fox (6.269 and 230) and Huntington (6.290 and 224). All use weight in pounds, ET in seconds and speed in mph.
Worked Example
Which Number to Trust
Trap speed is usually the better horsepower indicator, because ET depends heavily on traction, launch and shifting. If the ET method gives a much lower number than the trap speed method, the car is losing time at the launch. These formulas assume a typical street car's drivetrain loss and aerodynamics, so treat them as estimates.
Formula Constants
| Source | ET Constant | Trap Constant |
|---|---|---|
| Hale (1980s) | 5.825 | 234 |
| Fox | 6.269 | 230 |
| Huntington (1950s) | 6.290 | 224 |
Constants as compiled by Omni Calculator's quarter-mile reference.