Quarter Mile Calculator
Predict how a car runs the quarter mile from its weight and power, or work backward to estimate horsepower from a time slip. Pick the Fox, Hale or Huntington equation, switch between crank and wheel power, and see the eighth-mile ET and 60-foot launch time alongside the quarter-mile result.
Formula
Worked example
A 3000 lb car with 300 crank hp (Fox): W/P = 3000 / 300 = 10, so ET = 6.269 × 10^(1/3) = 6.269 × 2.154 ≈ 13.50 s. Trap speed = 230 × (300/3000)^(1/3) = 230 × 0.464 ≈ 106.7 mph, and the eighth mile is about 13.50 × 0.6363 ≈ 8.59 s. Reverse it: a 13.50 s slip at 3000 lb implies P = 3000 × (6.269 / 13.50)³ ≈ 300 hp.
The power-to-weight equations: Fox, Hale and Huntington
The quarter mile, a standing-start drag race over 1320 feet (402 metres), has a remarkably tidy relationship to a car's power-to-weight ratio. Several authors fitted empirical equations of the form ET = a × (W/P)^(1/3) for elapsed time and v = b × (P/W)^(1/3) for trap speed, where W is the vehicle weight in pounds and P is horsepower. Roger Huntington's 1950s fit used a = 6.290 and b = 224; Geoffrey Fox refined it to a = 6.269 and b = 230; and Patrick Hale, drawing on later software and faster cars, used a = 5.825 and b = 234. You can pick any of the three here. They are statistical fits to thousands of real runs rather than derivations from first principles, yet they predict times for typical cars surprisingly well, and comparing them brackets the likely range.
Crank power, wheel power and the reverse solve
The constants were calibrated against flywheel (crank) horsepower, so if you only have wheel horsepower from a dyno, this calculator converts it back to crank by dividing out an assumed driveline loss (about 11% for a manual, more for an automatic or all-wheel drive). You can also run the math backward: enter your weight and a measured ET or trap speed from a time slip, and the tool rearranges the equation to estimate the crank horsepower that produced it, since P = W × (a / ET)³ and P = W × (v / b)³. That reverse mode is a quick sanity check on a dyno number or a way to gauge a build from track results alone.
Eighth mile, 60-foot and why a cube root
Beyond the quarter mile, the tool estimates the eighth-mile ET (empirically about 64% of the quarter-mile time) and a rough 60-foot launch time (around ET divided by 7.2), so you can compare against an eighth-mile track or judge how much your start is costing you. The cube-root form of the main equations reflects the physics of accelerating to a velocity over a fixed distance at roughly constant power: it takes an eightfold improvement in power-to-weight to halve the elapsed time or double the trap speed. That is why shaving 200 lb or adding 30 hp produces a noticeable but modest gain, and why chasing ever-quicker times demands progressively larger changes to the ratio.
What the estimate leaves out
These equations assume an idealized run with good traction, well-timed shifts and a clean launch, so treat the output as a baseline rather than a guarantee. Real elapsed times are shaped by tire grip and launch quality, drivetrain losses, transmission gearing, aerodynamic drag at the top end, air density and even track preparation. A heavy car with sticky tires can beat its prediction off the line, while a powerful car that spins its tires will fall short. The eighth-mile and 60-foot figures are rules of thumb that vary with how a car puts its power down, so use them as ballparks.
Typical quarter-mile times by category
| Vehicle type | Quarter-mile ET | Bracket |
|---|---|---|
| Top-fuel dragster | ~3.7 s | Supercar |
| Modern supercar | 10-11 s | Very quick |
| Muscle / sports car | 12-14 s | Sporty |
| Hot hatch / sport sedan | 14-15 s | Sporty |
| Family sedan | 15-17 s | Everyday |
| Economy commuter | 17-19 s | Everyday |
Approximate ranges for stock vehicles; individual results vary with traction and conditions.
Frequently asked questions
Which equation should I use: Fox, Hale or Huntington?
All three are empirical fits to real drag-strip data, just calibrated against different cars and eras. Fox (6.269 / 230) is a common middle-ground choice, Huntington (6.290 / 224) leans slightly conservative on trap speed, and Hale (5.825 / 234) tends to predict quicker times for modern, well-launched cars. Running all three brackets the likely range rather than relying on a single number.
Can I work out horsepower from my quarter-mile time?
Yes. Switch to the reverse mode, enter your race weight and a measured ET or trap speed from a time slip, and the calculator rearranges the equation to estimate crank horsepower: P = W × (a / ET)³ from the time, or P = W × (v / b)³ from the speed. It is a good sanity check on a dyno figure.
Should I enter crank horsepower or wheel horsepower?
The constants were calibrated against flywheel (crank) horsepower. If you only have wheel horsepower from a dyno, choose "wheels" and the calculator converts it to crank by dividing out a driveline loss (about 11% for a manual, 15% or more for an automatic or all-wheel drive), so the prediction stays consistent with the equations.
How accurate are these quarter-mile formulas?
For typical street cars they land within a few tenths of a second of real-world times. They were fitted to thousands of runs but assume good traction and clean shifts, so cars with poor grip, heavy drivetrain losses or strong aerodynamic drag can deviate noticeably. The eighth-mile and 60-foot outputs are rules of thumb and vary more than the quarter-mile figure.