Quarter Mile Calculator
Estimate quarter-mile ET and trap speed from weight and horsepower using Roger Huntington's classic drag-racing formulas.
How it works
ET = 6.290 × (weight ÷ hp)^(1/3) · Trap speed = 224 × (hp ÷ weight)^(1/3)
These are Roger Huntington’s well-known drag-racing rules of thumb, which tie elapsed time (ET) and trap speed to the car’s power-to-weight ratio through a cube-root relationship. Elapsed time is the seconds from the start line to the quarter-mile mark; trap speed is how fast the car is going as it crosses it. The formulas assume a competent launch and reasonable traction, and they were calibrated on flywheel (crank) horsepower, so using wheel horsepower gives slightly conservative numbers. They are a solid ballpark for a well-set-up car but cannot capture tires, gearing, aero or the driver, so treat them as estimates.
Worked example
For a 3,300 lb car with 250 hp, the weight-to-power ratio is 13.2. Its cube root is about 2.37, so ET ≈ 6.290 × 2.37 ≈ 14.88 s. The power-to-weight ratio 0.0758 has a cube root near 0.423, giving a trap speed of about 224 × 0.423 ≈ 94.7 mph.
Frequently asked questions
Should I use crank or wheel horsepower?
Huntington’s formulas were built around crank (flywheel) horsepower. Wheel horsepower is lower after drivetrain losses, so plugging it in yields slightly slower, more conservative predictions.
Why does trap speed matter more than ET to some racers?
Trap speed depends mainly on power-to-weight and is less affected by how well you launch, so it is often seen as a cleaner measure of a car’s power. ET rewards traction and a good launch as well.
How accurate are these estimates?
They are good ballparks for a well-tuned car with decent traction, often within a few tenths on ET and a few mph on trap speed. Poor traction, tall gearing or a weak launch can make the real ET noticeably slower.
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Educational estimate. Real-world results vary with conditions, tuning and measurement.