Quarter Mile Calculator

General Physics

Calculate a vehicle's quarter-mile elapsed time and trap speed.

Examples

See some practical examples of quarter mile calculations.

Modern Muscle Car

etAndSpeed

Calculate ET and speed for a typical modern muscle car.

Tuned Sports Car

etAndSpeed

Calculate ET and speed for a lightweight, tuned sports car.

Classic Drag Car

horsepower

Estimate the horsepower of a classic drag car based on its weight and ET.

Unknown Weight Vehicle

weight

Estimate the weight of a vehicle from its known horsepower and ET.

Other Titles
Understanding the Quarter Mile Calculator: A Comprehensive Guide
An in-depth look at the principles behind quarter-mile performance calculations.

What is Quarter Mile Performance?

  • The Drag Strip Standard
  • Key Performance Metrics
  • Factors Influencing Performance
Quarter-mile performance is a benchmark used in drag racing to measure a vehicle's acceleration. It represents the time it takes for a vehicle to travel a distance of a quarter-mile (402 meters) from a standing start. This calculator uses a common formula to estimate two key metrics: Elapsed Time (ET) and Trap Speed.
The Drag Strip Standard
The quarter-mile has been the universal standard for measuring street car performance and professional drag racing for decades. It's a test of pure acceleration, combining engine power, traction, and vehicle weight into a single, comparable number.
Key Performance Metrics
Elapsed Time (ET) is the primary metric, indicating how quickly the car covers the distance. Trap Speed is the vehicle's speed at the moment it crosses the quarter-mile finish line, indicating the car's horsepower and aerodynamic efficiency.

Step-by-Step Guide to Using the Quarter Mile Calculator

  • Selecting Your Calculation
  • Inputting the Data
  • Interpreting the Results
This tool is designed for flexibility, allowing you to calculate performance, horsepower, or weight.
Step 1: Select Your Calculation Type
Use the dropdown menu to choose what you want to find: 'ET & Trap Speed', 'Horsepower', or 'Vehicle Weight'. The input fields will change based on your selection.
Step 2: Input the Required Data
Fill in the visible fields with your vehicle's data. For 'ET & Trap Speed', you'll need vehicle weight and horsepower. For 'Horsepower', you'll need weight and elapsed time. For 'Vehicle Weight', you'll need horsepower and elapsed time. Ensure you use the correct units (lbs, hp, seconds).
Step 3: Interpreting the Results
After clicking 'Calculate', the estimated results will appear. These values are based on an idealized formula and represent the vehicle's potential under optimal conditions (perfect traction, sea-level altitude, etc.).

Real-World Applications of the Quarter Mile Calculator

  • Performance Tuning
  • Vehicle Comparison
  • Project Car Planning
This calculator is more than a toy; it's a valuable tool for automotive enthusiasts.
Performance Tuning
Tuners can use the calculator to predict how changes in weight (e.g., removing seats) or horsepower (e.g., engine mods) will affect their quarter-mile times before hitting the track.
Vehicle Comparison
Easily compare the theoretical performance of different cars by inputting their stock weight and horsepower figures. This helps in understanding the power-to-weight ratio's importance.
Project Car Planning
When building a project car, you can set a target ET and use the calculator to estimate the required horsepower for a given weight, helping you budget and choose the right components.

Common Misconceptions and Correct Methods

  • Formula Limitations
  • Drivetrain Loss
  • Real-World Variables
It's important to understand what this calculator can and cannot do.
Formula Limitations
The formula used is an empirical one, derived from real-world data, but it is still an approximation. It assumes a rear-wheel-drive car with good traction and doesn't account for drivetrain type (FWD, AWD), transmission, or aerodynamics.
Drivetrain Loss
The horsepower input should ideally be 'wheel horsepower' (WHP), but most manufacturers state 'crank horsepower' (CHP). There is a power loss through the drivetrain (typically 15-20%). For more accuracy, use an estimated WHP value.
Real-World Variables
Driver skill, tire quality, track conditions, air density, and altitude all have a significant impact on actual quarter-mile times. The calculator provides a baseline, not a guaranteed result.

Mathematical Derivation and Formulas

  • The Czock Formula
  • Calculating Elapsed Time
  • Calculating Trap Speed
The calculations are based on formulas developed by Kenneth R. Czock, which provide a solid estimate based on the power-to-weight ratio.
The Core Formulas
Elapsed Time (ET) is calculated as: ET = 5.825 * (Weight / Horsepower)^(1/3)
Trap Speed is calculated as: Trap Speed = 234 * (Horsepower / Weight)^(1/3)
Reverse Calculations
The calculator can also rearrange these formulas to solve for horsepower or weight if you provide an ET. For example, to find Horsepower: HP = Weight / (ET / 5.825)^3

Example Calculation

  • For a car weighing 3500 lbs with 500 hp:
  • ET = 5.825 * (3500 / 500)^(1/3) = 5.825 * (7)^(1/3) ≈ 5.825 * 1.913 ≈ 11.14 seconds.
  • Trap Speed = 234 * (500 / 3500)^(1/3) = 234 * (0.1428)^(1/3) ≈ 234 * 0.523 ≈ 122.3 mph.