How quarter-mile time depends on power and weight
A car's acceleration over the quarter mile depends mostly on its power-to-weight ratio. Drag racers have long used two simple formulas, based on the cube root of weight per horsepower, that give a surprisingly good estimate for cars with decent traction.
Quarter mile formulas
Trap speed (mph) = 234 × ∛(horsepower ÷ weight)
Weight in pounds with the driver, horsepower at the wheels
Worked example
A 3,600 lb car with 400 wheel horsepower has 9 lb per hp. Its estimated quarter mile is 12.12 seconds at 112.5 mph. Adding 10% more power cuts it to about 11.74 seconds, and taking 200 lb out of the car to about 11.89 seconds.
Typical quarter-mile times
| Weight per wheel hp | Estimated ET | Estimated trap speed |
|---|---|---|
| 20 lb/hp | 15.8 s | 86.2 mph |
| 15 lb/hp | 14.4 s | 94.9 mph |
| 12 lb/hp | 13.3 s | 102.2 mph |
| 9 lb/hp | 12.1 s | 112.5 mph |
| 7 lb/hp | 11.1 s | 122.3 mph |
| 5 lb/hp | 10.0 s | 136.8 mph |
Why real times differ
- Traction: wheelspin at launch can add half a second or more; trap speed is less affected.
- Gearing and shifts: automatic and dual-clutch transmissions often beat the formula.
- Air density: hot, humid or high-altitude days make engines weaker.
Already have a time slip? Work backwards to horsepower with the horsepower calculator.
Frequently asked questions
How do you calculate quarter-mile time from horsepower?
Divide the weight in pounds by the wheel horsepower, take the cube root and multiply by 5.825. A 3,600 lb car with 400 wheel hp runs about 12.1 seconds.
How much horsepower do I need to run a 10-second quarter mile?
Roughly one wheel horsepower for every 5 pounds of weight. A 3,000 lb car with driver needs about 600 wheel horsepower and good traction.
Should I use crank or wheel horsepower?
The formulas are based on wheel horsepower. If you only know the brochure (crank) number, subtract about 10% to 15% for drivetrain losses.
Is losing weight as good as adding power?
In the formula, cutting 1% of weight helps as much as adding 1% of power. On a 3,600 lb car, 200 lb is about 5.6%, which is like adding 22 hp to a 400 hp car.
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Last updated October 2026.