Quarter Mile Calculator
How fast will your car run the quarter-mile? This calculator uses the classic Huntington formula to estimate elapsed time (ET) and trap speed from horsepower and weight. A 300 HP car weighing 3,500 lbs runs roughly a 13.5-second quarter at about 104 mph. It is an estimate, not a guarantee, since traction, gearing, and driver skill all affect real-world times.
The formulas
- ET (seconds) = 5.825 × (weight / HP)^(1/3)
- Trap speed (mph) = 234 × (HP / weight)^(1/3)
These come from the Huntington/Yates empirical models developed from thousands of drag strip runs. They assume reasonable traction and a competent driver. Modified cars with slicks and good launches often beat the predicted ET by 0.5 seconds or more.
Example predictions
- 200 HP, 3,000 lbs: 15.1 sec @ 90.3 mph
- 400 HP, 3,500 lbs: 12.7 sec @ 112.3 mph
- 500 HP, 3,800 lbs: 12.0 sec @ 118.6 mph
- 700 HP, 4,000 lbs: 10.9 sec @ 131.2 mph
What affects real-world results
- Traction: The biggest variable. Street tires on a cold track lose 1-2 seconds. Drag slicks and a prepped surface close the gap to the formula.
- Gearing: Tall highway gears hurt acceleration. Short gears with a proper converter stall or clutch drop improve times.
- Altitude: Higher altitude means less air for the engine. Expect about 3% power loss per 1,000 feet of elevation.
- Launch technique: Automatic vs. manual, converter stall speed, and clutch engagement all matter.
HP at the crank vs. wheels: Dyno sheets usually show wheel HP. Drivetrain loss is about 15% for manual transmissions and 18-20% for automatics. If using wheel HP, the formula will slightly underpredict the ET since it was calibrated for crank HP.