Quarter-Mile ET & Trap Speed Calculator
Compare estimated elapsed time and trap speed for your build.
Estimates use flywheel horsepower; wheel horsepower is converted using your selected driveline loss. The 60-foot range is a rough proportion of quarter-mile ET. Traction, gearing, air density, and launch technique affect real results.
How to estimate quarter-mile ET and trap speed
- Enter race-ready weight in pounds, including driver, fuel and anything carried during the run.
- Enter horsepower and select wheel or flywheel HP. The calculator converts wheel HP to estimated flywheel HP using your selected driveline loss.
- Choose Hale, Fox or Huntington to compare the model assumptions.
- Calculate quarter-mile elapsed time and trap speed. The eighth-mile and 60-foot figures are rough secondary estimates.
Formulas used by this calculator
Quarter-mile ET (seconds) = ET constant × ∛(weight ÷ flywheel HP)
Trap speed (MPH) = speed constant × ∛(flywheel HP ÷ weight)
| Model | ET constant | Speed constant |
|---|---|---|
| Hale | 5.825 | 234 |
| Fox | 6.269 | 230 |
| Huntington | 6.290 | 224 |
These are the coefficients implemented in this tool. Comparing models shows how an estimate changes; averaging them does not produce a measured result.
Flywheel HP = wheel HP ÷ (1 − driveline loss as a decimal)
For example, 300 wheel HP with an assumed 11 percent loss converts to approximately 337 flywheel HP. The default loss is an adjustable assumption, not a measurement of your drivetrain.
Example: 3,200 pounds and 300 flywheel horsepower
With the Hale selection, the estimate is 12.82 seconds at approximately 106.3 MPH. Select flywheel HP for this example; entering 300 as wheel HP produces a different result because the calculator applies the loss conversion.
What changes a real drag-strip result?
Traction, launch technique, shift timing, gearing, power delivery, weather and aerodynamic drag are not modeled individually here. ET is particularly sensitive to the launch. Use this tool to compare weight and power scenarios, then compare the estimates with actual timing slips.
The eighth-mile estimate divides quarter-mile ET by the selected factor, initially 1.56. The displayed 60-foot range is 14–16 percent of quarter-mile ET. Both are rough proportions, not independent simulations of acceleration.
Drag racing calculator questions
Should I enter curb weight?
Use total weight in running condition with the driver. Curb weight alone can omit a meaningful part of the load the engine must accelerate.
Should I choose wheel or flywheel horsepower?
Choose the basis of the number you actually have. Chassis-dyno results normally represent wheel power; engine-dyno results represent engine output. Do not apply driveline loss twice.
Is trap speed the same as top speed?
No. Trap speed describes speed near the end of a timed quarter-mile run. It is not the vehicle's maximum sustainable speed.
Will adding horsepower always match this prediction?
No. If the additional power overwhelms traction or changes the usable power band, the actual ET may improve less than the formula suggests.
Related calculators and workshop references
Return to all automotive calculators, check original specifications in the automotive manual library, or browse hot rod parts and workshop tools.