Quarter Mile ET Calculator
Calculate quarter-mile elapsed time (ET) and trap speed from vehicle weight and horsepower using Hale's formula.
Includes drivetrain loss and altitude correction.
Quarter Mile Elapsed Time — Hale’s Formula
Hale’s formula is the most widely used empirical formula for predicting quarter-mile performance based on power-to-weight ratio alone.
Elapsed Time (ET) ET (seconds) = 6.269 × (Weight / Wheel_HP)^(1/3)
Trap Speed Trap speed (mph) = 234 × (Wheel_HP / Weight)^(1/3)
Where Weight is the total vehicle weight in pounds (including driver and fuel), and Wheel_HP is the power actually delivered to the wheels after drivetrain losses.
Drivetrain Loss Engine dyno output is not the same as wheel power. Power is lost to friction in the transmission, driveshaft, differential, and axles. Typical losses:
- Front-wheel drive (FWD): ~15% loss
- Rear-wheel drive (RWD): ~12% loss
- All-wheel drive (AWD): ~20% loss
- Race / direct drive: ~5% loss
Altitude Correction Air density decreases with altitude. Combustion engines lose approximately 3% power per 1,000 feet (300 m) of elevation. Supercharged and turbocharged engines are less affected.
Power-to-Weight Ratio A key metric in performance: the lower the weight-to-power ratio (lb/hp), the faster the vehicle. Sports cars typically target 8–12 lb/hp. Supercars reach 4–6 lb/hp. Dragsters can achieve under 2 lb/hp.
Formula Limitations Hale’s formula assumes ideal traction, proper launch technique, and optimum conditions. Real-world results vary based on driver skill, tire grip, track preparation, gear ratios, and aerodynamics.