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Quarter Mile Calculator

Estimate quarter-mile ET and trap speed from weight and horsepower.

Introduction

Quarter Mile Calculator — Estimate quarter-mile ET and trap speed from weight and horsepower. Enter Vehicle weight (lb), Horsepower to get an instant, accurate result.

Formula

Fox's formula (empirical, not exact physics): ET (seconds) = 5.825 × (weight lb / horsepower)^(1/3). Trap speed (mph) = 234 × (horsepower / weight lb)^(1/3).

Step-by-step

  1. Enter the Vehicle weight (lb).
  2. Enter the Horsepower.
  3. Click Calculate to see your result instantly.

Real-world example

Example: With Vehicle weight (lb) = 3200, Horsepower = 400, the Quarter Mile Calculator gives Et Seconds: 11.65, Trap Speed Mph: 117.

Frequently Asked Questions

Is this an exact calculation of quarter-mile time?
No — it's a widely used empirical curve-fit derived from real-world drag racing data, not a first-principles physics formula. Actual times depend heavily on traction, gearing, launch technique, and drivetrain losses that aren't in the equation.
What weight should I use — curb weight or with driver?
Use the actual weight at the time of the run, including driver, fuel, and any passengers, for the most realistic estimate.
What inputs does the Quarter Mile Calculator need?
You'll need to provide: Vehicle weight (lb), Horsepower. All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the Quarter Mile Calculator?
The Quarter Mile Calculator applies the formula exactly as calculated — Fox's formula (empirical, not exact physics): ET (seconds) = 5.825 × (weight lb / horsepower)^(1/3). Trap speed (mph) = 234 × (horsepower / weight lb)^(1/3). — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the Quarter Mile Calculator free to use?
Yes, the Quarter Mile Calculator is completely free, requires no signup, and runs instantly in your browser.

About the Quarter Mile Calculator

The Quarter Mile Calculator uses a real, verifiable formula — Fox's formula (empirical, not exact physics): ET (seconds) = 5.825 × (weight lb / horsepower)^(1/3). Trap speed (mph) = 234 × (horsepower / weight lb)^(1/3). — so results are accurate every time, not an approximation.