Free Live Calculators

Quarter Mile Calculator: ET & Trap Speed Estimator

Estimate quarter-mile elapsed time and trap speed from weight and horsepower, or solve for the horsepower needed to hit a target ET.

Calculation Mode

Horsepower Basis

Estimated ET
13.08 sec
Estimated Trap Speed
104.2 mph

Rule-of-thumb estimate, not a physics simulation. These formulas ignore aerodynamic drag, tire traction, launch technique, gearing, and drivetrain type. All-wheel-drive and high-traction cars routinely beat this prediction; high-power or poor-traction cars often run slower than predicted. Real quarter-mile results vary — use this as a ballpark, not a guarantee.

ET = 5.825 × (Weight ÷ Horsepower)^(1/3). Trap Speed = 234 × (Horsepower ÷ Weight)^(1/3). Weight includes the driver. These are the standard rule-of-thumb constants used across drag-racing forums and calculators, attributed to Roger Huntington and refined by drag-racing analyst Patrick Hale.
88% found this helpful

Reference Values

Last verified:
Category Range What It Means Status
Elapsed Time (ET) formula ET = 5.825 × (Weight ÷ Horsepower)^(1/3) Weight in lb (including driver), horsepower at the flywheel/crank. Result is estimated quarter-mile elapsed time in seconds. The 5.825 constant is the standard version attributed to drag-racing analyst Roger Huntington. Good
Trap Speed formula Trap Speed = 234 × (Horsepower ÷ Weight)^(1/3) Same inputs as the ET formula. Result is estimated speed in mph at the end of the quarter-mile (the "trap"). The 234 constant pairs with the 5.825 ET constant in the same rule-of-thumb model. Good
Crank vs. wheel horsepower Wheel HP ≈ Crank HP × 0.80–0.85 The formulas were derived using flywheel/crank horsepower. Dyno-measured wheel horsepower (after drivetrain loss) will predict a slower, more conservative ET if used directly — know which number you're entering. Okay
Street car / stock sedan 13.5–16.0 sec ET, 90–100 mph trap Typical unmodified daily-driver sedans and compact cars, roughly 150–220 hp at 3,200–3,600 lb. Okay
Performance car / muscle car 12.0–13.5 sec ET, 105–115 mph trap Modern V8 muscle cars and tuned sport compacts in the 350–450 hp range. Good
High-power sports car 10.5–12.0 sec ET, 115–130 mph trap Sports cars and lightly modified performance cars in the 400–600 hp range at sub-3,500 lb. Good
Supercar / drag-built ★ 8.5–10.5 sec ET, 130–160+ mph trap Factory supercars and dedicated drag builds exceeding 600–1,000+ hp. Formula accuracy drops here because launch traction and aerodynamics dominate more of the result. ★ Best
All-wheel-drive / high-traction accuracy note N/A — model doesn't account for drivetrain AWD cars consistently beat this formula's ET prediction because superior launch traction isn't captured in a weight/power-only model. Treat AWD results as a conservative (slower) estimate. Poor

Source: Standard drag-racing rule-of-thumb ET/trap-speed formulas (constants 5.825 and 234), widely cited and attributed to drag-racing analyst Roger Huntington, refined and republished by Patrick Hale/Stealth316.com. See Hotrodders.com formula reference and Stealth316.com formulas page.

Worked Examples

Stock Daily-Driver Sedan

Weight
3,400 lb (with driver)
Horsepower
200 hp (crank)
14.98 sec ET, 91.0 mph trap

ET = 5.825 × (3,400 ÷ 200)^(1/3) = 5.825 × 17^(1/3) = 5.825 × 2.571 = 14.98 sec. Trap = 234 × (200 ÷ 3,400)^(1/3) = 234 × 0.0588^(1/3) = 234 × 0.389 = 91.0 mph.

Modified Sport Compact

Weight
3,000 lb (with driver)
Horsepower
300 hp (crank)
12.55 sec ET, 108.6 mph trap

ET = 5.825 × (3,000 ÷ 300)^(1/3) = 5.825 × 10^(1/3) = 5.825 × 2.154 = 12.55 sec. Trap = 234 × (300 ÷ 3,000)^(1/3) = 234 × 0.464 = 108.6 mph.

Muscle Car Build

Weight
3,800 lb (with driver)
Horsepower
450 hp (crank)
11.86 sec ET, 114.9 mph trap

ET = 5.825 × (3,800 ÷ 450)^(1/3) = 5.825 × 8.444^(1/3) = 5.825 × 2.037 = 11.86 sec. Trap = 234 × (450 ÷ 3,800)^(1/3) = 234 × 0.491 = 114.9 mph.

Lightweight Sports Car

Weight
2,800 lb (with driver)
Horsepower
400 hp (crank)
11.14 sec ET, 122.3 mph trap

ET = 5.825 × (2,800 ÷ 400)^(1/3) = 5.825 × 7^(1/3) = 5.825 × 1.913 = 11.14 sec. Trap = 234 × (400 ÷ 2,800)^(1/3) = 234 × 0.523 = 122.3 mph. Lower weight, not just higher power, is why this beats the heavier muscle car build above despite less horsepower.

Reverse Mode — Horsepower Needed for a Target ET

Weight
3,400 lb (with driver)
Target ET
11.0 sec
≈505 hp required (crank)

Solving the ET formula for horsepower: HP = Weight ÷ (ET ÷ 5.825)^3 = 3,400 ÷ (11.0 ÷ 5.825)^3 = 3,400 ÷ (1.888)^3 = 3,400 ÷ 6.732 ≈ 505 hp. Verifying: 5.825 × (3,400 ÷ 505)^(1/3) = 11.00 sec.

How to Use This Calculator

  1. 1

    Choose your mode

    "ET & Trap Speed" solves forward from weight and horsepower. "HP Needed for Target ET" solves backward from a goal time.

  2. 2

    Enter vehicle weight

    Total weight in pounds, including the driver — this matters as much as horsepower in the formula.

  3. 3

    Enter horsepower (or target ET)

    In forward mode, enter horsepower and note whether it's a crank/flywheel or wheel-dyno number. In reverse mode, enter the ET you're trying to hit instead.

  4. 4

    Read your estimate

    Updates instantly — forward mode shows elapsed time and trap speed; reverse mode shows the horsepower required and the trap speed that comes with it.

What Each Value Means

Elapsed Time (ET) (seconds)
The total time, in seconds, to cover a standing-start quarter mile (1,320 ft) — the primary metric used to rank drag-racing performance.
Trap Speed (mph)
The vehicle's speed at the finish line (the "trap"), a secondary metric that reflects horsepower more directly than ET does, since it's less sensitive to launch traction.
Weight-to-Power Ratio (lb per hp)
Vehicle weight divided by horsepower (lb/hp) — the single number both formulas are built around, since a lower ratio always predicts a quicker run.

Related Calculators

Frequently Asked Questions

How accurate is a quarter-mile calculator like this one?
It's a rule-of-thumb estimate, not a physics simulation — expect it to land within a few tenths of a second for a typical street car with average traction, but real results vary more than that. The formula only knows weight and horsepower; it has no idea about your tires, launch technique, gearing, aerodynamics, altitude, or track surface, all of which shift the real number up or down. Treat the output as a ballpark for comparing builds, not a guaranteed time slip.
Why do real-world results vary so much from the estimate?
Two cars with identical weight and horsepower can run very different ETs because the formula can't see traction, aerodynamic drag, gearing, or driver skill. A car that can't put power down cleanly off the line (wheelspin, poor launch) will run slower than predicted, while a car with excellent traction — especially all-wheel-drive — will often beat the prediction. High-power or low-traction vehicles see the widest gaps, since the formula assumes an idealized, consistent launch that real cars rarely achieve every run.
Should I use crank horsepower or wheel horsepower?
This formula was originally built around crank (flywheel) horsepower, the number on a manufacturer spec sheet or engine dyno. Wheel horsepower from a chassis dyno already has drivetrain loss subtracted (typically 15–20% for a manual RWD car, more for AWD), so plugging wheel hp straight into the crank-based formula predicts a slower ET than the car will actually run. If you only have a wheel-hp number, either convert it back toward crank hp first (divide by roughly 0.80–0.85) or treat the calculator's output as a conservative, slower-than-real estimate.
Why does a lighter, less powerful car sometimes beat a heavier one with more horsepower?
Elapsed time depends on the ratio of weight to power, not on horsepower alone — the formula uses weight ÷ horsepower, so cutting weight helps exactly as much as adding power does, pound for pound. A 2,800 lb car with 400 hp (7 lb/hp) will out-run a 3,800 lb car with 450 hp (8.4 lb/hp) despite having 50 less horsepower, because it has less mass for each unit of power to accelerate. This is the same reason race teams chase weight reduction as aggressively as they chase engine output.
Can I use this for motorcycles or AWD cars?
You can enter the numbers, but expect the AWD and motorcycle results to be less reliable than a typical RWD/FWD car. Motorcycles have an extreme power-to-weight ratio and traction/wheelie dynamics the formula doesn't model at all. AWD cars launch with far more usable traction than the weight/power-only formula assumes, so they consistently run quicker than predicted. Use the output as a rough floor estimate for these vehicle types rather than a close prediction.