Drag racers have long used empirical formulas linking power-to-weight ratio to quarter-mile performance. They are a quick way to estimate what an engine upgrade or weight reduction will do – or to estimate horsepower from a timeslip.
How to use the Quarter Mile Calculator
- Equation
- Weight (with driver)
- Power
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose a formula, then enter the race weight of the car with driver and the engine power at the flywheel. Traction, gearing and aerodynamics make real runs vary by a few tenths.
Inputs explained
| Field | What to enter |
|---|---|
| Equation | Choose one: Huntington, Fox, Hale |
| Weight (with driver) | Units: lb, kg, t, US ton |
| Power | Units: hp, kW, W |
Example values
How the main result changes when Weight changes and everything else stays at the example values above:
| Weight (with driver) (lb) | Quarter-mile elapsed time (s) |
|---|---|
| 1,750 | 10.288 |
| 2,625 | 11.776 |
| 3,500 | 12.961 |
| 4,375 | 13.962 |
| 5,250 | 14.837 |
| 7,000 | 16.33 |
Formula
Huntington: ET = 6.290·(W/P)¹/3), trap = 224·(P/W)¹/3) · Fox: ET = 6.269·(W/P)¹/3)
Hale: ET = 5.825·(W/P)¹/3), trap = 234·(P/W)¹/3) (W in lb, P in hp, speed in mph)
Worked example
Inputs — Equation: Huntington; Weight (with driver): 3,500 lb; Power: 400 hp.
Results — Quarter-mile elapsed time = 12.961 s; Trap speed = 108.7 mph; Power-to-weight ratio = 114.286 hp per 1,000 lb.
Key terms
- Elapsed time (ET)
- Time to cover a quarter mile from a standing start.
- Trap speed
- Speed at the finish line.
Frequently asked questions
How accurate are these formulas?
Usually within a few tenths of a second for well-launched cars.
Which formula should I use?
Huntington and Fox suit typical street cars; Hale gives faster times.
Can I estimate horsepower from my timeslip?
Yes – rearranging gives hp = W·(trap/224)³.
Why does weight matter so much?
Acceleration depends on force divided by mass.