About the Quarter Mile Calculator
This quarter mile calculator predicts how quickly a car can cover a standing 1/4 mile (402 m) and how fast it will be going through the traps, using only two numbers: race weight and horsepower. It uses the well-known Hale formulas that drag racers have relied on for decades to sanity-check a build before it hits the strip.
Use it to see what a power upgrade or weight reduction might be worth, to compare cars on paper, or to check whether a time slip matches the power you think you are making. You can also work backwards: a car that traps much slower than predicted is probably making less power than claimed.
Enter race weight including the driver and fuel, and flywheel (crank) horsepower. The result assumes a good launch, traction and gearing; real ET depends heavily on tyres, launch technique, altitude and weather, while trap speed tracks power much more closely.
With the default inputs, the estimated 1/4-mile et is 12 s. Change any value above to recalculate instantly.
How to use the quarter mile calculator
- 1Enter the race weight of the car including the driver and fuel.
- 2Pick pounds or kilograms.
- 3Enter crank horsepower (convert wheel horsepower first if needed).
- 4Read the estimated ET and trap speed, then use the chart to see what more power would do.
Formula and method
These are Roger Hale’s empirical drag-racing formulas. Acceleration depends on power-to-weight, and the cube root reflects the fact that aerodynamic drag grows rapidly with speed, so each extra horsepower buys a little less time. Weight is race weight in pounds (car, driver and fuel) and P is flywheel horsepower.
The formulas assume a well-sorted car with a clean launch. Trap speed is the more reliable figure because it depends mainly on power; ET also depends on traction, gearing and reaction to the launch. The 1/8-mile ET uses the common drag-strip conversion factor of 1.5832.
- ET
- Elapsed time over 1/4 mile (seconds)
- W
- Race weight in pounds, including driver
- P
- Flywheel (crank) horsepower
Worked examples
3,500 lb car with 400 hp
Weight-to-power is 3,500 ÷ 400 = 8.75 lb/hp. The cube root of 8.75 is 2.06, so ET ≈ 5.825 × 2.06 = 12.00 s and trap speed ≈ 234 ÷ 2.06 = 113.6 mph — typical of a modern V8 muscle car.
3,000 lb hot hatch with 300 hp
At 10 lb/hp the cube root is 2.154, giving an ET of about 12.55 s and a trap speed of about 108.6 mph (174.8 km/h).
1,500 kg sedan with 250 hp
1,500 kg is 3,307 lb, so the car carries 13.2 lb per horsepower. That predicts a quarter mile of about 13.8 s at roughly 99 mph.
Frequently asked questions
How accurate is a quarter mile calculator?+
For a well-driven car with good traction, the Hale formula is usually within a few tenths of a second on ET and a few mph on trap speed. Street tyres, wheelspin, altitude and heat can easily add half a second or more.
Should I use wheel horsepower or crank horsepower?+
The formula was built around flywheel (crank) horsepower. If you only have a chassis dyno number, convert it to crank horsepower first, typically by dividing by 0.85 for a rear-wheel-drive car.
Can I estimate horsepower from my time slip?+
Yes. Trap speed is the better guide: horsepower ≈ weight × (trap mph ÷ 234)³. A 3,500 lb car trapping 113.6 mph works out to about 400 hp.
What weight should I enter?+
Use the race weight — the car as it runs down the track with the driver and fuel on board. Leaving out a 180 lb driver makes the prediction noticeably too optimistic.
How do I convert quarter-mile ET to 1/8-mile ET?+
Divide the quarter-mile ET by about 1.5832, the conversion factor used widely at drag strips. A 12.00 s quarter-mile car should run roughly 7.58 s in the eighth mile.