Quarter Mile ET Calculator
Predict elapsed time and trap speed from weight and power.
Enter your values
Enter the vehicle weight with driver in lb.
Enter the wheel horsepower in hp.
Enter the target et in s.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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)
At a glance
| What it does | Predict elapsed time and trap speed from weight and power. |
|---|---|
| Category | Auto |
| Inputs needed | Vehicle weight with driver, Wheel horsepower, Target ET |
| Main output | Estimated quarter-mile ET |
| Formula | ET = 5.825 × (weight/hp)^(1/3) |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Vehicle weight with driver(lb)
- Enter the vehicle weight with driver in lb.
- Wheel horsepower(hp)
- Enter the wheel horsepower in hp.
- Target ET(s)
- Enter the target et in s.
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.
What do I need to enter into the Quarter Mile ET Calculator?
Just 3 values: vehicle weight with driver, wheel horsepower, target et. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Quarter Mile ET Calculator work out the answer?
The Fox equation estimates quarter-mile ET as 5.825 × (weight ÷ horsepower)^(1/3), with trap speed from 234 × (hp ÷ weight)^(1/3). It applies the formula ET = 5.825 × (weight/hp)^(1/3) and shows the working so you can check each step by hand.
Is the Quarter Mile ET Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.