Quarter-Mile ET Predictor Calculator
Elapsed time from weight and horsepower.
About this calculator
This calculator predicts quarter-mile elapsed time (ET) and trap speed from a vehicle's weight-to-power ratio, using the widely cited drag-racing formulas commonly attributed to Roger Huntington: ET = 5.825 x (weight / wheel horsepower)^(1/3), and trap speed (mph) = 234 / (weight / wheel horsepower)^(1/3). Both are empirical correlations fit to real drag-strip data rather than derived from first-principles physics, which is why they predict typical, well-driven passenger and performance vehicles reasonably well but can drift for outlier setups (very light cars, all-wheel drive launches, or forced-induction cars with unusual torque curves). The calculator first converts flywheel horsepower to wheel horsepower by subtracting a drivetrain-loss percentage -- typical figures run around 15% for a manual transmission, 18% for an automatic, and closer to 10% for a direct-drive or EV powertrain -- because it's wheel power, not crank power, that actually accelerates the car.
From the predicted ET, it also derives a 60-foot launch time (tire type changes this factor, since drag slicks launch harder than street tires), a rough 0-60 mph estimate, and eighth-mile ET/speed using commonly used fixed ratios to the full quarter-mile numbers. Treat every output here as a ballpark estimate for comparing setups, not a guaranteed track result -- real elapsed time depends heavily on driver skill, track surface, weather, and gearing that this simplified weight-and-power model doesn't capture.
Inputs
Results
Quarter-mile ET (sec)
13.54
Trap speed (mph)
100.7
How to Use This Calculator
- Enter Vehicle weight (lbs), Flywheel HP, and Drivetrain loss (%).
- Set Tire Type (Street or Drag Slick).
- Review Quarter-mile ET (sec) and Trap speed (mph).
- Use 60-ft time (sec) and Est. 0-60 mph (sec) to inform your decision.
How the result changes with Flywheel HP
| Flywheel HP | Quarter-mile ET (sec) | Trap speed (mph) |
|---|---|---|
| 150 | 17.06 | 79.9 |
| 225 | 14.9 | 91.5 |
| 450 | 11.83 | 115.3 |
| 750 | 9.97 | 136.7 |
What each input means
- Vehicle weight (lbs)
- Total vehicle weight including driver (curb weight + ~170 lbs).
- Flywheel HP
- Flywheel (crank) horsepower as rated by the manufacturer or measured on an engine dyno.
- Drivetrain loss (%)
- Typical losses: 15% manual, 18% automatic, 10% direct drive / EV.
- Tire Type
- Street tires have higher 60-ft times; drag slicks improve launch.
What each result means
- Quarter-mile ET (sec)
- Predicted elapsed time using ET = 5.825 × (W/WHP)^(1/3).
- Trap speed (mph)
- Estimated speed at the end of the quarter mile.
- 60-ft time (sec)
- Estimated 60-foot launch time based on tire type.
- Est. 0-60 mph (sec)
- Rough 0-60 estimate from quarter-mile ET.
- 1/8-mile ET (sec)
- Eighth-mile elapsed time (ET × 0.632).
- 1/8-mile speed (mph)
- Estimated speed at the 1/8-mile mark.
- Wheel HP
- Horsepower at the wheels after drivetrain loss.
- Lbs per WHP
- Weight-to-power ratio used in the calculation.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersVehicle weight (lbs) = 3200, Flywheel HP = 300, Drivetrain loss (%) = 15, Tire Type = 0 = 4 input(s) provided
- Calculate Quarter-mile ETQuarter-mile ET = 5.825 * pow(wpr, 1 / 3)13.536 = 13.536
- Calculate Trap speedTrap speed = 234 / pow(wpr, 1 / 3)100.7 = 100.7
- Calculate 60-ft time60-ft time = etSeconds * sixtyFootFactor2.058 = 2.058
- Calculate Est. 0-60 mphEst. 0-60 mph = etSeconds * 0.476.36 = 6.36
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the formula use weight divided by power instead of power divided by weight?
Acceleration depends on how much mass has to be moved by how much power, so a heavier car with the same power takes proportionally longer to cover the same distance. The cube-root relationship in the Huntington formula reflects how kinetic energy and drag losses scale over a quarter mile of acceleration, not a simple linear ratio -- it's an empirical fit to real timing-slip data, not a derived physics equation.
Why convert flywheel horsepower to wheel horsepower first?
The horsepower rating on an engine dyno or manufacturer spec sheet is measured at the crankshaft, before the transmission, driveshaft, and differential all consume some of that power through friction. The car only accelerates on the power that actually reaches the tires, so the calculator applies a drivetrain-loss percentage to estimate that wheel horsepower figure before predicting elapsed time.
How much does tire type actually change the results?
Tire type only changes the 60-foot time estimate in this calculator (a lower factor for drag slicks versus street tires), which reflects how much better slicks grip during the initial launch. It does not change the overall quarter-mile ET or trap speed prediction, since those are driven purely by the weight-to-power ratio in the Huntington formula.
Why might my car's actual quarter-mile time differ from this prediction?
The Huntington formula is an empirical average fit to typical drag-strip runs, so it doesn't account for driver launch technique, track prep and surface grip, altitude and weather (which change actual power output), gearing and shift points, or all-wheel-drive traction advantages. Use the prediction to compare relative changes -- like the effect of adding horsepower or shedding weight -- rather than as a guaranteed number.
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