Quarter Mile Calculator
Estimate 1/4-mile elapsed time and trap speed
Use vehicle weight and power to predict drag race performance with Huntington, Fox, or Hale empirical equations.
Performance Results
Performance Metrics
Introduction / Overview
This Quarter Mile Calculator estimates two drag racing staples: Elapsed time (ET) and Trap speed over a 1/4-mile (402.3 m) run. You provide a vehicle’s Weight and Power, and the calculator returns a first-order performance estimate using one of three well-known empirical formula families.
🎯 What it helps with: planning a target Elapsed time, estimating the impact of a power upgrade, and seeing how weight reduction might translate into faster runs — without needing a full vehicle dynamics model.
Who typically uses this?
- Weekend drag racers comparing setups (tire, gearing, bolt-ons) before spending time and money.
- Builders doing “back-of-the-napkin” checks when swapping engines, adding boost, or reducing weight.
- Curious car folks who want a quick estimate of Elapsed time / Trap speed from published power figures.
If you’re browsing other tools, the “Related Calculators” section on this page is a handy way to chain calculations (for example: unit conversions, physics calculators, and other performance estimators).
How to Use / Quick Start Guide
You can use this calculator in two directions: predict Elapsed time + Trap speed from Weight + Power, or estimatePower from a measured run (Elapsed time or Trap speed) and a known Weight.
Pick an equation (Huntington, Fox, or Hale)
If you’re unsure, Fox is a solid default. Huntington is the classic early version, and Hale tends to predict slightly quicker Elapsed times for the same power-to-weight.
Enter vehicle Weight (include the driver)
Use the weight you actually race at. A quick way to be “close enough” is curb weight + driver + fuel + any track-day gear.
Enter Power
Use horsepower (hp) if you have it, or enter kilowatts (kW) and let the calculator convert. For best results, use the power available during the run (drivetrain losses, heat soak, and tune all matter).
Read the results (Elapsed time + Trap speed)
Example input: 3,400 lb and 450 hp (Fox)
Output (estimate): Elapsed time ≈ 12.30 s and Trap speed ≈ 117 mph
How to interpret the numbers
- Elapsed time (ET) is the total time from start to the 1/4-mile finish.
- Trap speed is the speed at the finish line. It is often more stable than Elapsed time when traction or launch quality varies.
Performance Metrics & Power-to-Weight Ratio
The core of drag racing performance lies in the relationship between Power and Weight. This is expressed as the Power-to-Weight Ratio (PWR).
What is PWR?
Power-to-Weight Ratio measures how much power is available to move each unit of the vehicle's mass. In our calculator, we display this in two common formats:
- hp/lb: Horsepower per pound (common in US)
- hp/ton: Horsepower per metric ton (common globally)
Why it Matters
A higher PWR means the engine has less weight to push, leading to faster acceleration (lower Elapsed time) and higher top speeds (Trap speed). All the formulas used in this calculator (Huntington, Fox, Hale) are essentially different mathematical models of how PWR translates into 1/4 mile performance.
Calculation Method / Formula Explanation
All three options use the same basic shape: Elapsed time scales with the cube root of Weight-to-Power, and Trap speed scales with the cube root of Power-to-Weight. These formulas are mathematical models of how the Power-to-Weight Ratio (PWR) translates into acceleration over a fixed distance.
Core form used by all three
ET = k × (W / P)1/3
Trap Speed = c × (P / W)1/3
Where W is Weight (lb), P is Power (hp), ET is in seconds, and Trap speed is in mph. The term P / W is your Power-to-Weight Ratio.
Variables, in plain English
- Weight (W): vehicle + driver + fuel (use “race weight” when possible).
- Power (P): peak power available during the run (wheel hp vs crank hp changes results).
- Elapsed time (ET): time over the quarter mile, heavily affected by launch and traction.
- Trap speed: speed at the finish, often a better “power indicator” than Elapsed time.
The equations are traditionally expressed in lb and hp, but this calculator accepts metric units too and converts internally.
Huntington’s quarter-mile ET and speed formulas
Huntington’s approach is the classic “fit the data” method: measure many real cars, plot performance versus power-to-weight, and capture the trend with a simple curve. It’s old-school, but still useful as a baseline.
Huntington
ET = 6.290 × (W / P)1/3
Trap Speed = 224 × (P / W)1/3
✅ When it’s handy: quick comparisons between vehicles or “before vs after” checks when you change only one thing (Power or Weight).
Fox’s quarter-mile time and speed equations
Fox revisited the same idea with a more physics-minded lens: weight and power dominate the story, but traction, aero drag, gearing, and drivetrain losses can move the real result around — especially ET.
Fox
ET = 6.269 × (W / P)1/3
Trap Speed = 230 × (P / W)1/3
A practical takeaway
If you’re trying to “back-calculate” Power from a real run, Trap speed is often less sensitive to launch technique than Elapsed time. That’s why many people treat Trap speed as the more reliable indicator of Power.
Hale’s quarter-mile speed and ET formulas
Hale’s work is associated with more detailed software models, but the simplified equations are popular because they stay easy to use. Compared to the other two, Hale often predicts a shorter Elapsed time for the same power-to-weight.
Hale
ET = 5.825 × (W / P)1/3
Trap Speed = 234 × (P / W)1/3
⚠️ Sanity check: if Hale’s Elapsed time looks “too quick to be true,” it may be because your real-world setup is traction-limited or Power falls off before the finish.
Comparison of the three equations (worked example)
Let’s run the same car through all three formulas so you can see the “spread.” The goal isn’t to crown a single winner — it’s to understand the range these estimates can produce.
Example inputs
- Weight: 3,400 lb
- Power: 450 hp
| Equation | Elapsed time (s) | Trap speed (mph) | How it tends to feel |
|---|---|---|---|
| Huntington | ≈ 12.35 | ≈ 114 | Classic baseline |
| Fox | ≈ 12.30 | ≈ 117 | Good modern default |
| Hale | ≈ 11.43 | ≈ 119 | Often the “optimistic” ET |
If all three are clustered, your estimate is probably stable. If they spread apart (especially Elapsed time), treat the result as a range and lean on Trap speed for a power-focused check.
Real-World Examples / Use Cases
Setting a realistic target
Background: you’re aiming for a 12-second slip.
Inputs: 3,000 lb and (reverse) Elapsed time = 12.0 s (Fox).
Result: power estimate ≈ 428 hp.
Use it to decide whether you need more power or less weight.
Power upgrade planning
Background: adding a tune and intercooler.
Inputs: 3,400 lb; power from 380 → 450 hp.
Result: Elapsed time and Trap speed both improve.
Use it to check if the upgrade is “worth it” for your goal.
Weight reduction tradeoffs
Background: removing 150 lb (wheels, seats, spare tire).
Inputs: same power; weight 3,300 → 3,150 lb.
Result: quicker Elapsed time and slightly higher Trap speed.
Use it to compare “pounds saved” versus “hp gained.”
Sanity-checking a dyno number
Background: dyno says 520 hp, but the slip feels slow.
Inputs: race weight + measured trap speed.
Result: reverse-solved power may highlight drivetrain loss or heat soak.
Use it as a quick reality check.
Comparing two cars fairly
Background: two cars have very different weights.
Inputs: both cars’ weight + power.
Result: Elapsed time / Trap speed estimates on the same scale.
Use it to compare “potential” before launch skill and traction enter the picture.
Tips & Best Practices
Use race weight, not brochure weight
Driver weight, fuel, wheels/tires, and gear can add up. If you’re off by 200 lb, the estimate won’t be “wrong” — it will be answering a different question.
Prefer trap speed for “power checks”
ET is very sensitive to launch. Trap speed usually reflects sustained acceleration and power more consistently.
Be honest about usable power
Peak dyno power is great — but if the car can’t hold it (heat, boost taper, shift points), real Elapsed time may be slower.
Treat results as a range
Different equations and real-world conditions can move the outcome. If two formulas disagree, that’s a useful signal — not a bug.
Related Concepts / Background Info
Key terms you’ll hear at the track
- Elapsed time (ET): the clock time for the full 1/4-mile. Launch, traction, and shifting make a big difference.
- Trap speed: the speed at the finish line. It correlates strongly with average power delivered over the run.
- Wheel hp vs crank hp: drivetrain losses mean wheel horsepower is typically lower than advertised crank horsepower.
- Traction-limited launches: if tires spin, you can have great power but still record a slower Elapsed time.
🧠 A good mental model: Trap speed answers “how hard did the car pull overall,” while Elapsed time answers “how cleanly did everything happen, especially at the start.”
Frequently Asked Questions
Which equation should I choose?
If you want a simple default, start with Fox. Then toggle Huntington and Hale to see the range. If your build is traction-limited, Hale’s Elapsed time may be optimistic.
Do I enter wheel horsepower or crank horsepower?
Either can work — just be consistent. If you enter crank hp (advertised power), results can look faster than reality because drivetrain losses aren’t explicitly modeled.
Why is my predicted Elapsed time faster than what I run?
Common reasons include traction limits, conservative shifting, heat soak, altitude/weather, or using a weight that’s lighter than your real race setup.
Can I use this calculator in reverse to estimate horsepower?
Yes. Enter your vehicle Weight, then enter either Elapsed time or Trap speed and let the calculator solve for Power. Trap speed is often a smoother signal than Elapsed time.
Should I include the driver in the vehicle Weight?
Definitely. The formulas assume total moving Weight. Driver, fuel, and anything in the car during the run all count.
Why do the equations disagree?
They use the same cube-root relationship but different fitted constants. Think of them as slightly different “calibrations” from different eras and datasets.
What’s a “good” quarter-mile time?
It depends on the class and the vehicle. Use this calculator to compare your build against your own goals (before/after mods) rather than chasing a universal number.
Does this account for aerodynamics, gearing, tires, or track prep?
Not explicitly. That’s the tradeoff for a quick estimator. Those factors are why real runs can differ from the prediction.
Limitations / Disclaimers & Sources
- •This calculator provides estimates, not guaranteed results. Real Elapsed time and Trap speed depend on traction, shifting, aero drag, drivetrain efficiency, and conditions.
- •Power figures vary by measurement method (wheel vs crank), dyno type, correction factors, and temperature.
- •Use the results as a planning tool and a comparison baseline — not as professional performance advice.
External references (for deeper reading)
- P. Signell, "Static And Sliding Friction; Drag Racer Design," Dept. of Physics, Michigan State University (2000). [PDF Source]
- Wikipedia, "Power-to-weight ratio". [Link]
- Fox, G. (1973). "On the Physics of Drag Racing." The American Journal of Physics.
- Ryan, R. "Lessons in Systems Engineering – The SSME Weight Growth History." NASA. [PDF Source]
- Nightingale, N. P. (1986). "Automotive Stirling Engine – Mod II Design Report." NASA Lewis Research Center. [PDF Source]
- NASA Glenn Research Center. "High Power Density Solid Oxide Fuel Cell." [PDF Source]
- General Motors. (2008). "General Motors 2009 Data Book." [PDF Source]
- Cosworth. (2018). "Hypercar Engines: Aston Martin Valkyrie V12." [Link]
- Aston Martin. (2018). "Aston Martin Valkyrie V12 turns the hypercar engine up to 11,100." [Link]
- EngineLabs. (2015). "Test Shows Top Fuel Engine Makes 11,000+ Horsepower." [Link]
- Peukert, W. (1897). "Über die Abhängigkeit der Kapazität von der Entladestromstärke bei Bleiakkumulatoren." Elektrotechnische Zeitschrift, 20.
- Turner, M. J. L. (2018). "Rocket and Spacecraft Propulsion: Principles, Practice And New Developments." Springer Science & Business Media. ISBN 9783540221906.
Note: These formulas are widely circulated in motorsport contexts. The calculator uses the published constants as implemented in the equation selector.
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