acalculator

What is my 1/4 mile time?

Type your car’s race weight and flywheel horsepower. The 1/4 mile calculator estimates the quarter-mile elapsed time (ET) and trap speed; start from an ET or a trap speed instead to estimate the horsepower.

Your numbers

Units
Start from
Quarter-mile ET
12 s

A 3,500 lb car with 400 hp should run the quarter mile in about 12 s at 113.6 mph.

Trap speed
113.6 mph
Horsepower (at the flywheel)
400 hp
Pounds per horsepowerlb/hp
8.75

Quarter-mile ET: 12 s. A 3,500 lb car with 400 hp should run the quarter mile in about 12 s at 113.6 mph.

How to calculate

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.

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.

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.

  • 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).

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Start from Horsepower, Race weight 3,500 lb, Horsepower (at the flywheel) 400 hp gives Quarter-mile ET 12 s, Trap speed 113.6 mph, Pounds per horsepower 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. Start from Horsepower, Race weight 3,000 lb, Horsepower (at the flywheel) 300 hp gives Quarter-mile ET 12.55 s, Trap speed 108.6 mph.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. Start from ET, Race weight 3,200 lb, Quarter-mile ET 12 s gives Horsepower (at the flywheel) 366 hp, Trap speed 113.6 mph.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. Start from Trap speed, Race weight 3,400 lb, Trap speed 110 mph gives Horsepower (at the flywheel) 353 hp, Quarter-mile ET 12.39 s.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

How it works

Patrick Hale’s formulas estimate a quarter-mile pass from the race weight W (pounds, with driver and fuel) and the peak flywheel horsepower P:

  • ET (seconds) = 5.825 × (W ÷ P)^(1/3)
  • Trap speed (mph) = 234 × (P ÷ W)^(1/3)

Choose what to start from:

  • Horsepower: the ratio R = W ÷ P in pounds per horsepower, then ET and trap speed as above.
  • ET: R = (ET ÷ 5.825)³, then P = W ÷ R and the trap speed from R.
  • Trap speed: R = (234 ÷ mph)³, then P = W ÷ R and the ET from R.

The calculator shows the ET in seconds rounded to 2 decimal places, the trap speed in mph rounded to 1 decimal place (km/h in Metric), the flywheel horsepower rounded to a whole hp (kW in Metric), and the pounds per horsepower R rounded to 2 decimal places. Because both formulas use R, ET × mph = 5.825 × 234 = 1,363.05 for every input.

Units are converted with exact sizes (NIST SP 811): 1 lb = 0.45359237 kg, 1 hp = 550 ft·lbf/s = 745.69987158227 W, 1 PS = 735.49875 W, 1 mph = 0.44704 m/s, 1 km/h = 1/3.6 m/s.

Limits: weight 500 to 20,000 lb; horsepower 10 to 10,000 hp; ET 3 to 60 s; trap speed 20 to 400 mph.

Worked examples by hand

3,500 lb, 400 hp. R = 3,500 ÷ 400 = 8.75 lb/hp; 8.75^(1/3) = 2.06072. ET = 5.825 × 2.06072 = 12.00 s (12.0032); trap speed = 234 ÷ 2.06072 = 113.6 mph (113.5568).

3,000 lb, 300 hp. R = 10 lb/hp; 10^(1/3) = 2.15443. ET = 5.825 × 2.15443 = 12.55 s; trap speed = 234 ÷ 2.15443 = 108.6 mph.

ET 12.00 s at 3,200 lb. R = (12 ÷ 5.825)³ = 2.06009³ = 8.7429 lb/hp; P = 3,200 ÷ 8.7429 = 366 hp (366.011); trap speed = 1,363.05 ÷ 12 = 113.6 mph (113.5875).

Trap speed 110 mph at 3,400 lb. R = (234 ÷ 110)³ = 9.6266 lb/hp; P = 3,400 ÷ 9.6266 = 353 hp (353.191); ET = 1,363.05 ÷ 110 = 12.39 s (12.3914).

Other questions people ask

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.