Quarter Mile ET Calculator
Predict elapsed time and trap speed from weight and power.
Enter your values
ⓘ Live results
Results
- Estimated quarter-mile ET
- 11.89 s
- Trap speed
- 114.7 mph
- Power-to-weight
- 8.5 lb per hp
- Power needed for target ET
- 389 hp
- Eighth-mile estimate
- 7.61 s
Quick answer
The Fox equation estimates quarter-mile ET as 5.825 × (weight ÷ horsepower)^(1/3), with trap speed from 234 × (hp ÷ weight)^(1/3).
ET = 5.825 × (weight/hp)^(1/3)
How to use the Quarter Mile ET Calculator
- 1Weigh the car with fuel and driver, or use the curb weight plus 180 lb.
- 2Enter wheel horsepower — subtract about 15% from crank figures.
- 3Set a target ET to see the power required.
Worked example
Using the values the calculator loads with:
Inputs
- Vehicle weight with driver3400 lb
- Wheel horsepower400 hp
- Target ET12.0 s
Results
- Estimated quarter-mile ET11.89 s
- Trap speed114.7 mph
- Power-to-weight8.5 lb per hp
- Power needed for target ET389 hp
- Eighth-mile estimate7.61 s
Frequently asked questions
How accurate is the Fox equation?
For a street car with decent traction it is usually within 2–3 tenths. It assumes an average launch; poor traction or a slipping clutch will be slower.
Should I use crank or wheel horsepower?
Wheel horsepower gives better results. Drivetrain loss is typically 12–15% for manual and 15–20% for automatic transmissions.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.