Quarter Mile Calculator
Estimate quarter-mile ET and trap speed.
Results update as you type.
How it works
The quarter mile is the classic drag-racing benchmark, and this calculator estimates a vehicle's elapsed time (ET) and trap speed from its weight and horsepower. You enter the vehicle's weight and its horsepower, and it returns the estimated quarter-mile ET in seconds and the trap speed in miles per hour. The estimates use the well-established Fox and Hale formulas, which tie performance to the power-to-weight ratio: ET depends on the cube root of weight divided by power, and trap speed on the cube root of power divided by weight. The physics is intuitive — more horsepower accelerates the car harder, while more weight resists acceleration, so lighter, more powerful cars post quicker times and higher speeds. These formulas assume reasonably good traction and a typical drivetrain; real results vary with tires, launch technique, gearing, aerodynamics, elevation, and driver skill, so treat the output as a solid ballpark rather than a guarantee. Trap speed, the speed at the end of the quarter mile, is often considered a purer measure of power-to-weight than ET because it is less affected by launch and traction. This tool is popular for comparing builds, estimating the effect of adding power or shedding weight, and setting expectations before a track day. Enter your weight and horsepower to estimate your quarter-mile performance.
ET = 6.29 × (weight ÷ hp)^(1/3); trap = 224 × (hp ÷ weight)^(1/3)
These well-known drag-racing estimates relate quarter-mile performance to a car's power-to-weight ratio. The elapsed time uses the cube root of weight divided by horsepower, and the trap speed uses the cube root of horsepower divided by weight, so more power or less weight improves both.
Source:Fox & Hale drag-racing formulas
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter vehicle weight and horsepower.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Quarter-mile ET updates instantly as you type — no button to press.
Frequently asked questions
How is quarter-mile time estimated?
This calculator uses the Fox formula, which relates elapsed time to the power-to-weight ratio: ET equals 6.29 times the cube root of weight divided by horsepower. It captures the fundamental physics that more power and less weight yield quicker times. Real results vary with traction, gearing, and driving, so treat it as a close estimate.
What is trap speed?
Trap speed is the vehicle's speed as it crosses the end of the quarter mile. It is estimated as 224 times the cube root of horsepower divided by weight. Many enthusiasts consider trap speed a better indicator of a car's true power-to-weight than ET, since it is less influenced by launch traction and reaction time at the start.
Why does power-to-weight matter so much?
Acceleration depends on the force available relative to the mass being moved. More horsepower provides more accelerating force, while more weight demands more force for the same acceleration. The ratio of the two governs how quickly a car can cover the quarter mile, which is why both formulas depend on power-to-weight rather than power alone.
How accurate are these estimates?
They give a reliable ballpark for typical street and performance cars with reasonable traction, often within a few tenths of a second. However, tires, launch technique, transmission type, gearing, aerodynamics, air density, and driver skill all affect real runs. Use the estimate to compare setups or gauge the impact of changes, not as a precise prediction.
How much power do I need to improve my ET?
Because ET scales with the cube root of weight over power, gains diminish as power rises — going from 300 to 330 horsepower helps less than the first jumps. Reducing weight is often as effective as adding power. Use the calculator to try different weight and horsepower values and see how each change shifts your estimated ET.