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Tire Size Calculator

Decode a tyre size such as 225/45R17 into width, sidewall height and overall diameter.

How it works Report a problem


Tire Size Calculator

Calculate the exact physical dimensions of your tires.

Example Tire Code: 225 / 45 R 17

About the Tire Size Calculator

Decode a tyre size such as 225/45R17 into width, sidewall height and overall diameter.

How to use the Tire Size Calculator

  1. Enter the Tire Width (mm), Aspect Ratio (%) and Wheel Diameter (inches).
  2. Press Calculate Dimensions.

Formula and method

Sidewall = width × aspect ratio. Overall diameter = wheel diameter × 25.4 + 2 × sidewall (in mm).

Worked example

A 225/45R17 tyre has a sidewall of 101.25 mm and an overall diameter of 634.3 mm.

Tips

  • Keep the overall diameter within about 3% of the original so the speedometer stays accurate.

Frequently asked questions

What does 225/45R17 mean?
225 mm wide, sidewall height 45% of the width, radial construction, fits a 17-inch wheel.