GARAGE CALCS FOR THE HOME BUILDER

Quarter-mile ET and MPH calculator

Predict what your car should run from its weight and horsepower, or work backward from a timeslip to estimate how much power it's making.

Free, no sign-upUpdated September 2026
Your numbers
Car
I want to find

Result

1/4 mile ET
1/4 mile trap speed
1/8 mile ET
1/8 mile trap speed
Weight per horsepower

The formulas

Trap speed (mph) = 234 × (hp ÷ weight)1/3
ET (s) = 5.825 × (weight ÷ hp)1/3

These estimates, credited to Roger Huntington and Geoffrey Hale, have been used by racers for decades. Weight includes the driver. The horsepower they imply is roughly flywheel horsepower for a typical street car. Real results vary with traction, gearing, aerodynamics and weather.

The eighth-mile figures use common conversions: ET about ÷ 1.57 and trap speed about ÷ 1.26 from the quarter mile.