GarageCalc 
The formulas
This calculator uses the classic Hale drag-racing relationships: ET = 6.29 x (weight / horsepower)^(1/3) and trap speed = 224 x (horsepower / weight)^(1/3). They were derived from thousands of real timeslips and still hold remarkably well for anything with functional traction. The horsepower-from-trap mode simply inverts the second formula.
Traction is the main error source: launch-limited cars (high power, street tires, rear drive) run slower ETs than predicted while trapping close to the estimate. That gap between predicted and actual ET is effectively a traction meter. Compare your estimate against real tested times in our 0-60 times database.
Frequently asked questions
How accurate is a quarter mile calculator?
For a well-driven car with decent traction, the classic weight-to-power formulas land within a few tenths of real timeslips. They assume good launch conditions: an all-wheel-drive car with launch control may beat the estimate, while a high-power rear-drive car on street tires that struggles for traction will run slower than predicted.
What weight should I enter?
Race weight: the car as it runs, with driver and fuel. Curb weight plus roughly 200 lb for a driver and gear is a good approximation. Using the brochure curb weight alone makes the estimate optimistic.
Why is trap speed a better power indicator than ET?
Elapsed time depends heavily on the launch and traction; trap speed mostly reflects power-to-weight over the whole run. That is why the reverse mode here estimates horsepower from trap speed: it is the standard drag-strip method for sanity-checking dyno claims.
What is a fast quarter mile time?
For street cars: 15-16 s is typical commuter territory, 13-14 s is quick, 11-12 s is seriously fast (modern muscle and performance EVs), and anything under 11 s used to require slicks and a roll cage but is now stock Tesla Plaid or Cyberbeast territory.