How to Use Our Tyre Size Calculator

Simply input three numbers found on your tyre’s sidewall (e.g., 205/55R16):

Width (mm): The first number (e.g., 205).
Profile: The second number (aspect ratio percentage, e.g., 55).
Rim Diameter (in): The last number (e.g., 16).

Click “Calculate”, and instantly get:

Overall Diameter: Total height of the tyre.
Circumference: Distance covered in one full rotation.
Sidewall Height: Vertical measurement from rim to tread.
Revolutions per Mile/Kilometre: Spins needed to travel 1 mile/km.

How the Tyre Size Comparison Tool Works

Simply input your current tyre size and your proposed new size.

The tool will calculate the Diameter and Circumference Differences between the tyre tyres as well as providing a breakdown of the Overall Diameter, Circumference, Sidewall Height, Revolutions per Mile, and Revolutions per Kilometre or each tyre.

This tool is designed to help you quickly decode tyre dimensions, compare different tyre sizes, and ensure compatibility with your vehicle.

Whether you’re upgrading wheels, checking fitment, or simply curious about how tyre dimensions affect your driving experience, this calculator provides precise, user-friendly insights.

How to Use This Data

For replacements: Ensure new tyres have a diameter/circumference within 3% of the original to avoid speedometer errors.
For upgrades: A taller tyre (larger diameter) may improve fuel efficiency on highways but reduce acceleration responsiveness.
For technical adjustments: Use revolutions/km to program speed sensors or ECU settings.

Why This Matters

Even small size variations can alter handling, fuel efficiency, and safety. Always consult a professional if the comparison shows significant deviations.

Where to Find Your Tyre Size Numbers

Tyre size information is printed on the sidewall of your current tyres (and often in your vehicle’s manual or door jamb sticker). Here’s how to locate and interpret the code:

Check the Tyre Sidewall

Look for a string of letters and numbers like 205/45R17. This is your tyre’s size and specifications.

Section Width: The tyre’s width in millimetres (e.g., 205 mm).

Aspect Ratio: The sidewall height as a percentage of the section width (e.g., 55% of 205 mm).

Construction (R): “R” stands for Radial, the most common tyre type.

Rim Diameter (16): The wheel diameter in inches that the tyre fits (e.g., 17 inches).

Alternative Sources

If the sidewall is worn, check:

Your vehicle’s owner’s manual.
The driver’s door jamb sticker.
Fuel flap or glovebox documentation.