# What is my 1/4 mile time?

Estimates a car’s quarter-mile (1/4 mile) elapsed time and trap speed from its weight and horsepower with Hale’s formulas, or the horsepower from an ET or trap speed.

- Page: https://www.acalculator.org/sports/quarter-mile-calculator
- JSON spec: https://www.acalculator.org/sports/quarter-mile-calculator.json
- Version: 608899f5dbfd

## Default answer

Example with the default inputs (Start from Horsepower, Race weight 3,500 lb, Horsepower (at the flywheel) 400 hp): A 3,500 lb car with 400 hp should run the quarter mile in about 12 s at 113.6 mph.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| from | Start from | Estimate the ET and trap speed from the horsepower, or the horsepower from an ET or a trap speed. |
| w | Race weight | The car’s weight as it sits at the start line, with the driver and fuel. |
| hp | Horsepower (at the flywheel) | The engine’s peak power at the flywheel (crank), not at the wheels. |
| et | Quarter-mile ET | The elapsed time over the quarter mile from a time slip. |
| mph | Trap speed | The speed through the timing lights at the end of the quarter mile. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| et | Quarter-mile ET | Hale’s elapsed time: 5.825 × (pounds ÷ horsepower)^(1/3) seconds. |
| speed | Trap speed | Hale’s speed at the end of the quarter mile: 234 × (horsepower ÷ pounds)^(1/3) mph. |
| power | Horsepower (at the flywheel) | The flywheel horsepower that fits the weight and the ET or trap speed. |
| ratio | Pounds per horsepower | The race weight in pounds ÷ the flywheel horsepower. |

## Method

Hale: ET (s) = 5.825 × (weight in lb ÷ flywheel hp)^(1/3); trap speed (mph) = 234 × (hp ÷ lb)^(1/3); turned around, lb/hp = (ET ÷ 5.825)³ = (234 ÷ mph)³.

## Assumptions

- The weight is the race weight with driver and fuel, in pounds; the power is peak flywheel (crank) horsepower, not wheel horsepower.
- Hale fitted the constants to cars with good traction; a street car on street tires usually runs slower than the estimate.
- 1 hp = 550 ft·lbf/s = 745.699872 W; 1 lb = 0.45359237 kg; 1 mph = 0.44704 m/s (NIST SP 811).

## Worked examples

1. from = power, w = 1,587.573295, hp = 298,279.948633 gives et = 12.003243, mph = 50.764435, ratio = 8.75. Source: Patrick Hale’s quarter-mile formulas as given by Stealth 316, Formulas for 1/4 mile ET and mph vs. hp and weight (ET = 5.825 (weight/hp)^(1/3), MPH = 234 (hp/weight)^(1/3)), https://www.stealth316.com/2-calc-hp-et-mph.htm, retrieved 2026-10-02.
2. from = power, w = 1,360.77711, hp = 223,709.961475 gives et = 12.549582, mph = 48.554435. Source: Patrick Hale’s quarter-mile formulas as given by Stealth 316, Formulas for 1/4 mile ET and mph vs. hp and weight (ET = 5.825 (weight/hp)^(1/3), MPH = 234 (hp/weight)^(1/3)), https://www.stealth316.com/2-calc-hp-et-mph.htm, retrieved 2026-10-02.
3. from = et, w = 1,451.495584, et = 12 gives hp = 272,934.287514, mph = 50.778156. Source: Patrick Hale’s quarter-mile formulas as given by Stealth 316, Formulas for 1/4 mile ET and mph vs. hp and weight (ET = 5.825 (weight/hp)^(1/3), MPH = 234 (hp/weight)^(1/3)), https://www.stealth316.com/2-calc-hp-et-mph.htm, retrieved 2026-10-02.
4. from = speed, w = 1,542.214058, mph = 49.1744 gives hp = 263,374.345024, et = 12.391364. Source: Patrick Hale’s quarter-mile formulas as given by Stealth 316, Formulas for 1/4 mile ET and mph vs. hp and weight (ET = 5.825 (weight/hp)^(1/3), MPH = 234 (hp/weight)^(1/3)), https://www.stealth316.com/2-calc-hp-et-mph.htm, retrieved 2026-10-02.

## FAQ

### How do I estimate my quarter-mile time from horsepower?

Divide the race weight in pounds by the flywheel horsepower, take the cube root, and multiply by 5.825. A 3,500 lb car with 400 hp has 8.75 lb/hp; 8.75^(1/3) = 2.061, so the ET is about 5.825 × 2.061 = 12.00 seconds.

### How do I estimate trap speed?

Trap speed (mph) = 234 × (hp ÷ lb)^(1/3). For 400 hp and 3,500 lb that is 234 ÷ 2.061 = 113.6 mph.

### How do I find horsepower from my time slip?

Start from the ET or the trap speed. From ET: hp = weight ÷ (ET ÷ 5.825)³; a 12.00 s pass at 3,200 lb gives about 366 hp. From trap speed: hp = weight × (mph ÷ 234)³; 110 mph at 3,400 lb gives about 353 hp. Trap speed is usually the better guide, because a bad launch slows the ET far more than the speed.

### Is the horsepower at the flywheel or the wheels?

At the flywheel (the crank), as Hale used it. Wheel horsepower from a chassis dyno is lower because of drivetrain losses, so using it here would predict a slower car than you have.

### What weight should I use?

The race weight: the car as it sits at the start line, with the driver and fuel. Every 10% more weight per horsepower adds about 3% to the ET.

### How accurate are these estimates?

They are rough guides. Hale fitted the constants to cars with good traction, so a street car on street tires usually runs a few tenths slower. Gearing, launch, altitude and weather also change the time slip.

### Why do ET and trap speed always multiply to about 1,363?

Both formulas use the same weight-to-power ratio, once cubed-rooted and once inverted, so ET × mph = 5.825 × 234 = 1,363.05 for every car. A real time slip that is far off this number points to traction or launch trouble.

## Sources

- Stealth 316, Formulas for 1/4 mile ET and mph vs. hp and weight (Patrick Hale: ET = 5.825 (weight/hp)^(1/3), MPH = 234 (hp/weight)^(1/3); hp is peak engine output at the clutch, weight with driver), retrieved 2026-10-02. https://www.stealth316.com/2-calc-hp-et-mph.htm
- NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B.8 (pound = 0.45359237 kg, horsepower = 550 ft·lbf/s, mile per hour = 0.44704 m/s), retrieved 2026-10-02. https://www.nist.gov/pml/special-publication-811