Quarter Mile Calculator
Estimate a car's quarter mile time and trap speed from its weight and power, or work backwards to the power a target time needs.
🏁 What is a Quarter Mile Calculator?
A quarter mile calculator estimates how quickly a vehicle covers 1320 feet (402.336 metres) from a standing start, and how fast it is going at the finish. The two numbers drag racers care about are the elapsed time (ET), the clock time from launch to the finish line, and the trap speed, the speed recorded just before the line. This page produces both from a car's weight and power using widely quoted empirical rules of thumb, and offers a constant acceleration mode for the clean textbook case.
People use this kind of estimate to sanity-check a build, compare cars, set a performance goal or interpret a timeslip. If you know a car weighs 3200 lb and makes 300 hp, you can predict a ballpark ET of about 12.8 seconds and a trap speed near 106 mph. Working the other way, you can ask how much power a lighter or faster target needs. The same ideas help students connect power, mass and acceleration: more power per unit mass means a higher average acceleration and a shorter time.
It is important to be honest about accuracy. The ET and trap speed formulas used here, ET = 5.825 (weight / horsepower)^(1/3) and trap speed = 234 (horsepower / weight)^(1/3), were fitted to typical drag strip results. Sources disagree on who should be credited and on the exact coefficients, so the formulas are best described by their constants. They assume a reasonable launch, street-type tyres and a naturally aspirated engine, and they ignore gearing, traction, aerodynamics, altitude and weather. Treat every result as an estimate to within a few tenths of a second, or worse on a poor launch.
The constant acceleration mode uses the exact kinematics ET = sqrt(2 d / a) and v = a t, so it is a physics model, not an estimate of a particular car, but real vehicles do not accelerate at a constant rate. Related tools include the horsepower calculator, the acceleration calculator and the rolling resistance calculator, which shows how much of a car's power goes into tyre losses.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — A 3200 lb Car With 300 hp
Estimate for 3200 lb (with driver) and 300 hp
Example 2 — Metric Inputs: 1500 kg and 150 kW
Estimate for a 1500 kg car with 150 kW
Example 3 — A Lightweight 450 hp Sports Car
Estimate for 3500 lb and 450 hp
Example 4 — Power Needed for a 12 Second Pass
A 3000 lb car aiming for a 12.00 second quarter mile
Example 5 — Power Needed for a 10.5 Second Pass
A 2800 lb car aiming for a 10.50 second quarter mile
Example 6 — Constant Acceleration of 6 m/s²
An ideal car accelerating at a steady 6 m/s² over 402.336 m
Example 7 — Constant Acceleration of 0.8 g
An ideal launch at a steady 0.8 g
❓ Frequently Asked Questions
🔗 Related Calculators
How do you calculate quarter mile time from horsepower and weight?
A common rule of thumb is ET = 5.825 x (weight / horsepower)^(1/3), with weight in pounds including the driver. A 3200 lb car with 300 hp gives 5.825 x 10.667^(1/3) = 12.82 seconds. It is an estimate, not a guarantee.
How do you estimate quarter mile trap speed?
A common rule of thumb is trap speed in mph = 234 x (horsepower / weight)^(1/3), with weight in pounds. A 3200 lb car with 300 hp gives about 106.3 mph, or 171.1 km/h, at the end of the quarter mile.
How accurate are quarter mile calculators?
They are fitted to typical drag strip results and are usually within a few tenths of a second to about a second for ordinary cars on good tyres. Poor traction, gearing, altitude, heat and launch skill can move real times well beyond that.
How much horsepower do I need for a 12 second quarter mile?
Rearranging the rule of thumb gives hp = weight x (5.825 / ET)^3. A 3000 lb car needs about 343 hp to run 12.00 seconds. The power needed grows with the cube of the improvement, so a quicker time costs a lot more power.
Do I use crank horsepower or wheel horsepower?
The rule of thumb is generally quoted with engine (crank) horsepower. Wheel horsepower is lower because of drivetrain losses, often around 10 to 20 percent, so if you only have a dyno wheel figure the estimate will look slower than reality.
What is the difference between ET and trap speed?
Elapsed time (ET) is the time from leaving the start line to crossing the finish line, 1320 ft away. Trap speed is the speed measured over a short distance at the end of the run. ET depends on launch and traction, trap speed mainly on power over weight.
How is quarter mile time related to 0 to 60 time?
There is no exact conversion, because traction and gearing affect each differently. Roughly, a car that runs 0 to 60 mph in 5.5 seconds finishes the quarter mile around 13 seconds. The Constant acceleration mode shows the ideal 0 to 60 time for a given average acceleration.
How long is a quarter mile in feet and metres?
A quarter mile is 1320 feet, which is 402.336 metres or 0.4023 km. The calculator uses 402.336 m in constant acceleration mode, where ET = sqrt(2 x 402.336 / a).
What ET and trap speed come from a constant acceleration of 6 m/s2?
With a constant acceleration of 6 m/s2 the elapsed time is sqrt(2 x 402.336 / 6) = 11.58 s, and the final speed is 6 x 11.58 = 69.48 m/s, which is 155.4 mph. Real cars cannot hold constant acceleration for the whole run.
Why do two sources give different quarter mile formulas?
Several fitted coefficient sets circulate, and different websites attribute them to different people. The pair used here, 5.825 for ET and 234 for trap speed, is widely quoted, and other sets differ only slightly. Cite a formula by its constants, not just a name.