# Quarter Mile Calculator

Estimate quarter-mile elapsed time and trap speed from horsepower and vehicle weight. Uses the proven Huntington formula for drag strip performance.

## What this calculates

How fast will your car run the quarter-mile? This calculator uses the classic Huntington formula to estimate elapsed time (ET) and trap speed from horsepower and weight. A 300 HP car weighing 3,500 lbs runs roughly a 13.5-second quarter at about 104 mph. It is an estimate, not a guarantee, since traction, gearing, and driver skill all affect real-world times.

## Inputs

- **Horsepower** (HP) — min 1 — Engine horsepower at the crank (or wheel HP if known).
- **Vehicle Weight** (lbs) — min 100 — Total vehicle weight including driver (curb weight + ~170 lbs).

## Outputs

- **Elapsed Time (ET)** (sec) — Estimated quarter-mile elapsed time.
- **Trap Speed** (mph) — Estimated speed at the end of the quarter-mile.
- **Trap Speed** (km/h) — Trap speed in km/h.
- **Power-to-Weight Ratio** (HP/lb) — Horsepower per pound.

## Details

**The formulas:**

- **ET (seconds) = 5.825 × (weight / HP)^(1/3)**
- **Trap speed (mph) = 234 × (HP / weight)^(1/3)**

These come from the Huntington/Yates empirical models developed from thousands of drag strip runs. They assume reasonable traction and a competent driver. Modified cars with slicks and good launches often beat the predicted ET by 0.5 seconds or more.

**Example predictions:**
- **200 HP, 3,000 lbs:** 15.1 sec @ 90.3 mph
- **400 HP, 3,500 lbs:** 12.7 sec @ 112.3 mph
- **500 HP, 3,800 lbs:** 12.0 sec @ 118.6 mph
- **700 HP, 4,000 lbs:** 10.9 sec @ 131.2 mph

**What affects real-world results:**
- **Traction:** The biggest variable. Street tires on a cold track lose 1-2 seconds. Drag slicks and a prepped surface close the gap to the formula.
- **Gearing:** Tall highway gears hurt acceleration. Short gears with a proper converter stall or clutch drop improve times.
- **Altitude:** Higher altitude means less air for the engine. Expect about 3% power loss per 1,000 feet of elevation.
- **Launch technique:** Automatic vs. manual, converter stall speed, and clutch engagement all matter.

**HP at the crank vs. wheels:** Dyno sheets usually show wheel HP. Drivetrain loss is about 15% for manual transmissions and 18-20% for automatics. If using wheel HP, the formula will slightly underpredict the ET since it was calibrated for crank HP.

## Frequently Asked Questions

**Q: How accurate is this quarter-mile calculator?**

A: The Huntington formula is typically within 0.3 to 0.5 seconds of real-world times for stock or mildly modified vehicles. Heavily modified cars with drag slicks and optimal launches can beat the prediction by a full second or more. Factors like traction, gearing, altitude, and driving technique are not modeled.

**Q: Should I use crank HP or wheel HP?**

A: The formula was developed using crank (engine) horsepower. If you only have wheel dyno numbers, add about 15% for a manual or 20% for an automatic to estimate crank HP. Using wheel HP directly will give an optimistic (faster) prediction.

**Q: What weight should I use?**

A: Use the total weight of the vehicle as it sits on the track, including the driver, fuel, and any cargo. A good starting point is curb weight plus 170 lbs for the driver. Do not use dry weight or shipping weight.

**Q: Why do some cars beat the predicted time by a lot?**

A: Cars with exceptional traction (drag slicks on a prepped surface), high-stall torque converters, and experienced drivers can launch much harder than the formula assumes. Turbocharged cars with launch control and all-wheel drive are especially good at beating the formula.

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Source: https://vastcalc.com/calculators/physics/quarter-mile
Category: Physics
Last updated: 2026-04-08