Quarter Mile CalculatorQuarter Mile ET & Trap Speed Calculator (plus 1/8 Mile)
Quarter-mile ET ≈ 5.825 × (weight ÷ horsepower)^⅓ and trap speed ≈ 234 × (horsepower ÷ weight)^⅓
Predict your quarter-mile elapsed time and trap speed from horsepower and race weight, then see the eighth-mile equivalent. Works with crank or wheel horsepower and adjusts for altitude on naturally aspirated engines.
Race setup
400 hp at 3,600 lb.
Street car territoryET vs horsepower at your weight
Power adder table
| Horsepower | 1/4 ET | 1/4 trap | 1/8 ET |
|---|---|---|---|
| 400 (yours) | 12.12 s | 112.5 mph | 7.71 s |
| 450 (+50) | 11.65 s | 117.0 mph | 7.41 s |
| 500 (+100) | 11.25 s | 121.2 mph | 7.16 s |
| 550 (+150) | 10.90 s | 125.1 mph | 6.93 s |
| 600 (+200) | 10.58 s | 128.8 mph | 6.74 s |
| 700 (+300) | 10.05 s | 135.6 mph | 6.40 s |
How do you calculate quarter mile time from horsepower?
Quarter-mile ET ≈ 5.825 × (weight ÷ horsepower)^⅓ and trap speed ≈ 234 × (horsepower ÷ weight)^⅓ — the classic Huntington drag-racing formulas. A 3,600 lb car with 400 hp is predicted to run about 12.12 seconds at 112.5 mph, roughly 7.71 seconds in the eighth mile.
Part of our Engine & Performance calculators — for the core estimate, start with the Horsepower Calculator.
Quarter mile ET and trap speed formulas
1/4 mile trap speed = 234 × (hp ÷ weight lb)^(1/3)
1/8 mile ET ≈ 1/4 mile ET ÷ 1.5715
1/8 mile trap ≈ 1/4 mile trap ÷ 1.2245
Wheel HP → crank HP ≈ whp ÷ 0.85
Altitude (naturally aspirated) ≈ −3% power per 1,000 ft
The formulas assume good traction and a typical street-car setup. They are best at predicting trap speed, which depends mostly on power-to-weight; ET also depends on launch, gearing and tires.
Already have a timeslip? Work backward to horsepower with the Horsepower Calculator.
Example: 400 hp, 3,600 lb
| Measure | Calculation | Result |
|---|---|---|
| 1/4 ET | 5.825 × (3,600 ÷ 400)^⅓ | 12.12 s |
| 1/4 trap | 234 × (400 ÷ 3,600)^⅓ | 112.5 mph |
| 1/8 ET | 12.12 ÷ 1.5715 | 7.71 s |
| 1/8 trap | 112.5 ÷ 1.2245 | 91.9 mph |
These match the calculator’s defaults.
Horsepower vs weight: what’s worth more?
| Change from 400 hp / 3,600 lb | New ET | Improvement |
|---|---|---|
| −100 lb | 12.00 s | 0.11 s |
| +10 hp | 12.02 s | 0.10 s |
| +50 hp | 11.65 s | 0.47 s |
Gearing matters too — check engine RPM at the traps with the Gear Ratio Calculator.
NHRA safety requirements by ET
Faster cars need more safety equipment at NHRA-sanctioned tracks. Requirements tighten as ETs drop — for example, cars running quicker than certain thresholds (such as 11.49 and 9.99 seconds) need equipment like roll bars, roll cages, harnesses and approved helmets. Always check the current NHRA rulebook and your track’s tech requirements before racing.
Related calculators
Quarter Mile Calculator FAQs
Divide weight by horsepower, take the cube root and multiply by 5.825. 3,600 lb and 400 hp predicts about 12.1 seconds.
Divide horsepower by weight, take the cube root and multiply by 234. 400 hp at 3,600 lb predicts about 112.5 mph.
Multiply the eighth-mile ET by about 1.5715 and the eighth-mile trap speed by about 1.2245. These are common approximations.
At 3,500 lb, roughly 530 hp at the crank by these formulas. Lighter cars need less.
Yes. Thinner air reduces power, especially for naturally aspirated engines — often estimated at about 3% per 1,000 feet.
The classic formulas were built around crank (flywheel) horsepower. If you have dyno wheel horsepower, choose Wheel HP and the calculator converts it.
Poor launches, wheelspin, gearing, heat soak and weather can all add time. Trap speed is usually closer to the prediction than ET.
About the developer
Manzoor Ahmad
Web Designer & Calculator Developer · 13+ years of web development and SEO experienceI’m a professional pharmacist turned tech geek, and I designed and coded this quarter mile calculator myself. It uses the well-known Huntington formulas used by drag racers for decades, and it’s honest that trap speed is the more reliable prediction.
Found a number that looks wrong, or want a feature added? Tell me through my author page — corrections are fixed and re-dated.
Sources
- NHRA — Drag racing 101
- NHRA — Rulebook and tech information
- SAE International — J1349: Engine power test code
Disclaimer: Predictions assume good traction and typical conditions. Actual ET varies with launch, gearing, tires, weather and track prep. Race only at sanctioned facilities.
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