Quarter Mile Calculator: ET & Trap Speed
Enter your car's weight and horsepower to estimate standing-start quarter-mile elapsed time (ET) and trap speed. Compare three published formulas side by side, get an eighth-mile estimate, or run the math backwards to find the power you need for a target ET.
- Huntington (1958): ET = 6.290×(W/P)1/3
- Hale (1986): ET = 5.825×(W/P)1/3
- Fox (2000): ET = 6.269×(W/P)1/3
Your car
Use race weight: curb weight + driver + fuel + cargo. Power can be crank (flywheel) or wheel horsepower.
Results
All three formulas, side by side
| Formula | ET (s) | Trap (mph) | 1/8 ET (s) | 1/8 trap (mph) |
|---|---|---|---|---|
| Huntington (1958) | – | – | – | – |
| Hale (1986) | – | – | – | – |
| Fox (2000) | – | – | – | – |
Huntington is the conservative, most-quoted baseline. Hale is the optimistic end (well-prepped cars). Fox usually lands in between. Treat the three as an estimate range.
How much power do I need for a target ET?
Inverts the Huntington formula: power = weight / (ET / 6.290)3.
How much power do I need for a target trap speed?
Inverts the trap-speed formula: power = weight × (MPH / 224)3.
How light must my car be for a target ET with my power?
Inverts the ET formula: weight = power × (ET / 6.290)3.
What does your ET mean?
Simplified street/strip guide. Your latest result is highlighted. Class names and cutoffs vary by track and sanctioning body — this is a bench-racing guide, not an official rulebook.
| ET range | Typical trap | Class | What it means |
|---|---|---|---|
| 17.0+ s | < 85 mph | Daily driver | Economy cars, minivans, base trucks |
| 15.0 – 16.99 s | 85 – 95 mph | Average modern sedan | Family sedans, crossovers |
| 14.0 – 14.99 s | 95 – 100 mph | Warm street car | Sporty coupes, hot hatches |
| 13.0 – 13.99 s | 100 – 108 mph | Quick street car | Performance sedans, V8 coupes |
| 12.0 – 12.99 s | 108 – 115 mph | Fast street / muscle | Classic muscle, modern sports cars |
| 11.0 – 11.99 s | 115 – 125 mph | Serious street-strip | Modified builds; most tracks require a roll bar/cage under ~11.50 |
| 10.0 – 10.99 s | 125 – 135 mph | Pro street | Dedicated strip cars, big power |
| 9.0 – 9.99 s | 135 – 150 mph | Super pro | Race-only builds, full safety gear |
| under 9.0 s | 150+ mph | Pro competition | Dragsters, pro mods, purpose-built race cars |
Safety note: running 11.49 or quicker typically requires a roll bar or cage, a driveshaft loop, and more at most NHRA-sanctioned tracks. Always check your track's current rulebook before racing.
How the math works
The three formulas
- Huntington (1958) —
ET = 6.290 x (W/P)^(1/3),MPH = 224 x (P/W)^(1/3). W = weight in lb, P = power in hp. - Hale (1986) —
ET = 5.825 x (W/P)^(1/3),MPH = 234 x (P/W)^(1/3). - Fox (2000) —
ET = 6.269 x (W/P)^(1/3),MPH = 230 x (P/W)^(1/3).
Reverse solvers
- Power for a target ET:
P = W / (ET/6.290)^3 - Power for a target trap speed:
P = W x (MPH/224)^3 - Weight for a target ET:
W = P x (ET/6.290)^3
Eighth-mile estimate
ET_1/8 = ET_1/4 / 1.5832(conversion credited to Bobby Mosher)MPH_1/8 = MPH_1/4 x 0.80(rule-of-thumb approximation)
Wheel vs crank horsepower
crank hp = wheel hp / (1 - loss),wheel hp = crank hp x (1 - loss)- Presets: FWD ~10%, RWD ~15%, AWD ~20%. Modern drivetrains are often more efficient — measure on a dyno for a real number.
Attribution note
Some websites label the 6.290/224 constants as "Hale's formula". The published record shows otherwise: 6.290/224 is Roger Huntington's 1958 formula (ROD & CUSTOM magazine), while Patrick Hale's 1986 "Quarter Jr." formula uses 5.825/234, and Bob Fox's 2000 update uses 6.269/230. This calculator uses the historically correct attributions.
Scope boundary — what this tool does not do
- Not a 0–60 mph or 0–100 km/h calculator (different physics: launch traction dominates).
- Not a dyno: it estimates from rated power, it cannot measure your engine.
- Does not model gearing, tire size, shift points, aerodynamics, or density altitude.
- Does not predict bracket-racing dial-ins or reaction times.
- Does not estimate top speed or fuel economy.
Estimates only. Never race on public roads — take it to a sanctioned drag strip with proper safety equipment.
Frequently asked questions
What does a quarter-mile calculator estimate?
It estimates your elapsed time (ET) and trap speed over a standing-start quarter mile (1,320 feet / 402.3 meters) from just two inputs: vehicle weight and engine power. The estimates come from classic drag-racing power-to-weight formulas published by Roger Huntington (1958), Patrick Hale (1986), and Bob Fox (2000). Real times vary with traction, gearing, tires, weather, and driver skill.
What is the Huntington quarter-mile formula?
Huntington's formula is ET = 6.290 x (weight / power)^(1/3) for elapsed time in seconds, and trap speed = 224 x (power / weight)^(1/3) in mph, with weight in pounds and power in horsepower. Published by Roger Huntington in ROD & CUSTOM magazine in 1958, it is the oldest and most widely quoted of the three formulas in this calculator. Example: a 3,500 lb car with 400 hp gives ET of about 12.96 s and trap speed of about 108.7 mph.
What is the Hale formula, and how is it different?
Patrick Hale's 1986 formula uses ET = 5.825 x (weight / power)^(1/3) and trap speed = 234 x (power / weight)^(1/3). Compared with Huntington, Hale predicts quicker ETs and higher trap speeds for the same car - it was calibrated on 1980s drag data and tends to match well-prepped modern cars. This calculator shows all three formulas side by side so you can see the spread.
What is Fox's quarter-mile formula?
Bob Fox's 2000 formula uses ET = 6.269 x (weight / power)^(1/3) and trap speed = 230 x (power / weight)^(1/3). It was derived from late-1990s production-car data and usually lands between the Huntington and Hale predictions. Treat the three results as an estimate range rather than a single exact number.
How accurate are these calculators compared to real drag strip times?
Typically within about half a second and 5 mph for a car with decent traction - good enough for bench racing and build planning, not for predicting a specific pass. The formulas assume ideal traction and average conditions. A car that spins off the line, runs at high elevation, or has tall gearing will run slower than predicted; a prepped surface with slicks can run quicker.
Should I enter crank horsepower or wheel horsepower?
Enter whichever number you have, then set the power type toggle. Crank (flywheel) horsepower is what manufacturers quote; wheel horsepower is what a chassis dyno measures and is lower because of drivetrain loss. If you enter wheel horsepower, the calculator can convert it to crank horsepower using your drivetrain layout before applying the formulas.
How much power is lost through the drivetrain?
Typical drivetrain losses are about 10% for front-wheel drive, 12-15% for rear-wheel drive, and 18-22% for all-wheel drive, though modern cars are often more efficient. This calculator includes presets for each layout plus a custom percentage. The math is simple: crank hp = wheel hp / (1 - loss), so 400 whp through a 15% driveline equals about 471 crank hp.
How much horsepower do I need to hit a target ET?
Use the Reverse Solver tab: enter your target ET and vehicle weight, and it inverts the formula - power = weight / (ET / 6.290)^3. For example, a 3,500 lb car needs about 654 hp to run an 11.0-second quarter mile. You can also solve for the target trap speed or the maximum weight for a given power and ET goal.
How do I convert a quarter-mile ET to an eighth-mile ET?
A common conversion (credited to Bobby Mosher) is: eighth-mile ET = quarter-mile ET / 1.5832, and eighth-mile trap speed is approximately quarter-mile trap speed x 0.80. This calculator applies both automatically to every result. They are approximations - gearing and power delivery change the real ratio slightly from car to car.
What weight should I enter - curb weight or race weight?
Enter race weight: curb weight plus driver, fuel, and anything else in the car on the run. A 3,400 lb car with a 180 lb driver and a half tank of fuel is really racing at about 3,650 lb, which costs roughly 0.3 seconds. The calculator has quick-add chips for driver weight to make this easy.
What is a good quarter-mile time for a street car?
As a rough guide: 15-17 seconds is an average modern sedan, 13-14 is a quick street car, 12-13 is fast street or classic muscle territory, and anything under 12 seconds is a serious street-strip build. Under 11.5 seconds, most tracks require a roll bar or cage - check your local track's rulebook. The ET Classes tab maps your result onto this scale automatically.
Why does my car run slower than the calculator predicts?
The usual suspects are traction (street tires on an unprepped surface), density altitude (hot weather and elevation rob power - roughly 3% per 1,000 feet), tall or economy gearing, a heavy race weight you did not account for, or power measured optimistically. Fix traction first: most street cars lose half a second or more in the first 60 feet alone.
Can I use metric units?
Yes - toggle the weight unit between pounds and kilograms; power stays in horsepower, which is the unit all three formulas were published in. The calculator converts kilograms to pounds internally (1 kg = 2.20462 lb) before applying the formulas, so the results are identical either way.
Do these formulas work for motorcycles and EVs?
They work reasonably for anything with a power-to-weight ratio in the normal range, including motorcycles - just use the bike plus rider weight. For EVs, use peak power, but note the estimate may be optimistic at the top end because EV power tapers at high speed while the formulas assume a combustion-style power curve. Treat EV trap speeds as a best case.
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