Calculations use standard NHRA conversion factors (1.57 for ET, 1.24 for Speed).
Understanding 1/8 to 1/4 Mile Conversions
Drag racing takes place primarily on two distances: the eighth-mile (660 feet) and the quarter-mile (1320 feet). Many tracks across the country have switched to 1/8 mile racing due to space constraints, insurance requirements, or safety concerns regarding the high speeds achieved by modern performance vehicles in the full quarter-mile.
The 1/8 to 1/4 Mile Calculator helps racers and enthusiasts estimate their quarter-mile performance based on eighth-mile time slips. This is essential for tuning comparisons and benchmarking against vehicles that run on different tracks.
How the Calculation Works
While there is no perfect formula that accounts for aerodynamics, gearing, and tire size for every specific car, statistical averages provide highly accurate estimates for most street and bracket cars.
Elapsed Time (E.T.) Conversion: The most common conversion factor is 1.57. We multiply the 1/8 mile E.T. by 1.57 to get the 1/4 mile E.T. Faster, high-horsepower cars might use a lower factor (around 1.54-1.55), while slower street cars might be closer to 1.58.
Trap Speed (MPH) Conversion: Speed is typically converted by multiplying the 1/8 mile speed by a factor of 1.24 to 1.25. Vehicles with poor aerodynamics may see a lower multiplier, while streamlined vehicles may see a higher one.
Common Conversion Benchmarks
Below is a reference chart for common performance benchmarks using the standard 1.57 conversion factor.
1/8 Mile E.T.
Est. 1/4 Mile E.T.
Performance Tier
9.00 sec
14.13 sec
Stock Sport Compact
8.00 sec
12.56 sec
Modern Muscle Car
7.00 sec
10.99 sec
Modified Street/Strip
6.00 sec
9.42 sec
Dedicated Race Car
5.00 sec
7.85 sec
Pro Mod / Dragster
Factors Influencing the Conversion
If your actual quarter-mile time differs significantly from the calculator's estimate, consider the "Back Half" of the track (the distance between the 1/8 and 1/4 mile marks).
Aerodynamics: At speeds over 100mph, wind resistance increases exponentially. A car with poor aerodynamics (like a truck) will run a slower quarter-mile than the 1/8 mile conversion predicts.
Gearing: If a car runs out of gear (hits the rev limiter) before the finish line, the 1/4 mile MPH will suffer.
Power Adders: Turbocharged cars often pick up significant speed in the back half, potentially beating the estimated MPH, whereas nitrous setups often hit harder in the first half.
function calculateQuarterMile() {
// 1. Get input values by ID
var etEight = document.getElementById('etEight').value;
var mphEight = document.getElementById('mphEight').value;
// 2. Validate inputs
if (etEight === "" || isNaN(etEight) || etEight 0) {
var speedQuarter = parseFloat(mphEight) * speedFactor;
speedQuarterResult = speedQuarter.toFixed(2) + " MPH";
}
// 5. Display Results
var resultArea = document.getElementById('results-area');
var resultEtEl = document.getElementById('resultEt');
var resultMphEl = document.getElementById('resultMph');
resultArea.style.display = "block";
resultEtEl.innerHTML = etQuarter.toFixed(3) + " sec";
resultMphEl.innerHTML = speedQuarterResult;
}