Quarter-Mile ET Calculator
Estimate a car’s quarter-mile elapsed time and trap speed from its horsepower and weight using proven drag-racing formulas.
How it works
ET (s) = 5.825 × (weight ÷ hp)^(1/3) · Trap speed (mph) = 234 × (hp ÷ weight)^(1/3) — Hale’s equations
These are the classic empirical drag-strip formulas (Hale’s equations), which relate a car’s power-to-weight ratio to its quarter-mile elapsed time and trap speed. They work because acceleration over a fixed distance is governed largely by how much power moves how much mass. They assume decent traction and a competent launch, and they do not account for aerodynamics, gearing, tyre grip or driver skill — so a car that hooks up well can beat the estimate, while a poor launch or spinning tyres will fall short. Using wheel horsepower rather than crank horsepower gives the most realistic result.
Worked example
A 3,400 lb car making 300 hp has a weight-to-power ratio of 11.33. ET = 5.825 × 11.33^(1/3) = 5.825 × 2.246 ≈ 13.08 s, and trap speed = 234 × (300 ÷ 3400)^(1/3) ≈ 104 mph.
Frequently asked questions
Should I use crank or wheel horsepower?
Wheel horsepower gives a more realistic prediction, since that is the power actually reaching the road. If you only have the crank figure, subtract a drivetrain loss (about 15% for rear-wheel drive) first, or expect the estimate to be slightly optimistic.
Why does my real ET differ from the estimate?
These formulas assume a clean launch with good traction. Wheelspin, a slipping clutch, tall gearing, high air density or a heavy driver all slow you down, while sticky tyres and a perfect launch can beat the prediction. They are a planning guide, not a guarantee.
Does weight really matter that much?
Yes. Because ET scales with the cube root of weight-to-power, shedding weight is often as effective as adding power. Cutting 300 lb from a 3,400 lb car improves the ratio almost as much as adding roughly 25 hp.
Related calculators
Educational estimate — real figures vary by vehicle, load, conditions and manufacturer specs. Always follow your owner’s manual.