How do I calculate quarter-mile ET?

ET = 6.269 × (Weight ÷ Horsepower)^0.333. For a 3,500 lb car with 400 hp: ET = 6.269 × (3,500/400)^0.333 = 6.269 × (8.75)^0.333 = 6.269 × 2.063 = 12.93 seconds. This is an estimate — actual ET varies with traction, launch technique, and surface.

What is trap speed in drag racing?

Trap speed is the vehicle's speed at the quarter-mile finish line, measured by timing lights in the final 66 feet. It reflects sustained power delivery better than ET (which is influenced by launch). Trap speed = 234 × (HP ÷ Weight)^0.333.

What horsepower do I need to run a 10-second quarter mile?

For a 3,200 lb (street-weight) car, solving for HP at ET=10.0: 10.0 = 6.269 × (3,200÷HP)^0.333 → HP = 3,200 ÷ (10.0/6.269)^3 = 3,200 ÷ 5.84 = ~548 hp at the wheels (about 620–660 crank hp). Weight reduction or better traction can reduce the required power.

Is the Hale's quarter-mile formula accurate?

Within 0.3–0.5 seconds for most street cars under typical conditions. The formula is calibrated for vehicles with good traction and competent drivers. Cars with poor traction management, manual transmissions without launch control, or poorly tuned setups will run slower than predicted.

Quarter-Mile Calculator: ET and Trap Speed from Weight and Power

Estimate quarter-mile elapsed time (ET) and trap speed from vehicle weight and horsepower. Covers the HP method, the 1/4-mile formulas, and how modifications affect ET.

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Quarter-Mile Estimation Formulas

There are two main empirical formulas for estimating quarter-mile elapsed time (ET) and trap speed from vehicle weight and horsepower.

Hale's Formula (ET from weight and horsepower):

ET = 6.269 × (Weight ÷ Horsepower)^0.3333

Trap Speed (mph) = 234 × (HP ÷ Weight)^0.3333

These formulas assume optimal conditions (drag strip surface, good traction, experienced driver).

Worked Example

2024 Chevrolet Camaro ZL1 — 3,950 lbs, 650 hp, RWD:

ET: 6.269 × (3,950 ÷ 650)^0.333 = 6.269 × (6.077)^0.333 = 6.269 × 1.826 = 11.44 seconds - Factory claimed 1/4-mile: ~11.4 seconds ✓

Trap Speed: 234 × (650 ÷ 3,950)^0.333 = 234 × (0.1645)^0.333 = 234 × 0.549 = 128.5 mph

Understanding Trap Speed

Trap speed (the speed at the quarter-mile finish line) is a more reliable indicator of a vehicle's power-to-weight performance than ET, because ET is more affected by launch technique while trap speed reflects sustained power delivery.

The relationship between ET and trap speed:

Trap Speed ≈ 1,353 ÷ ET (approximate)

A car running 11.5-second quarters should have a trap speed around 118–122 mph if launching well. Significantly lower trap speed suggests poor traction or early wheel spin eating into the run.

Effect of Modifications on ET

Modification	Typical ET Improvement
+50 hp (bolt-ons)	−0.3 to −0.5 sec
+100 hp (forced induction)	−0.5 to −0.9 sec
Weight reduction (−200 lbs)	−0.3 to −0.5 sec
Drag radials (vs. street tires)	−0.3 to −0.7 sec
Launch control (if not equipped)	−0.2 to −0.5 sec
Engine break-in completion	−0.1 to −0.2 sec

Drag Strip Classes by ET

ET Range	Drag Racing Class
> 13.0 sec	Stock / Super Stock
11.5–13.0 sec	Street class
10.0–11.5 sec	High-performance street / Semi-Pro
8.5–10.0 sec	Pro Street / modified
< 8.5 sec	Race-built / Pro drag

For NHRA bracket racing, any ET can compete — the handicap system equalizes different ET cars.

Related Guides

Frequently Asked Questions

How do I calculate quarter-mile ET?: ET = 6.269 × (Weight ÷ Horsepower)^0.333. For a 3,500 lb car with 400 hp: ET = 6.269 × (3,500/400)^0.333 = 6.269 × (8.75)^0.333 = 6.269 × 2.063 = 12.93 seconds. This is an estimate — actual ET varies with traction, launch technique, and surface.
What is trap speed in drag racing?: Trap speed is the vehicle's speed at the quarter-mile finish line, measured by timing lights in the final 66 feet. It reflects sustained power delivery better than ET (which is influenced by launch). Trap speed = 234 × (HP ÷ Weight)^0.333.
What horsepower do I need to run a 10-second quarter mile?: For a 3,200 lb (street-weight) car, solving for HP at ET=10.0: 10.0 = 6.269 × (3,200÷HP)^0.333 → HP = 3,200 ÷ (10.0/6.269)^3 = 3,200 ÷ 5.84 = ~548 hp at the wheels (about 620–660 crank hp). Weight reduction or better traction can reduce the required power.
Is the Hale's quarter-mile formula accurate?: Within 0.3–0.5 seconds for most street cars under typical conditions. The formula is calibrated for vehicles with good traction and competent drivers. Cars with poor traction management, manual transmissions without launch control, or poorly tuned setups will run slower than predicted.

Last updated 7/28/2026