Your tyre size can be found on the sidewall of your current tyre and is a sequence of numbers and letters. For example 225/40/R18
When buying new tyres, you will need to make note of the following tyre size information from the sidewall of the existing tyre to ensure you select the correct replacement tyre for the vehicle.
The first 3 digits. This displays the width of the tyre. A tyre marked 225 will measure 225mm across the tread from sidewall to sidewall.
The 4th and 5th digits of the tyre code follow the tyre width. The profile height of the tyre sidewall is expressed as a percentage of the tyre width. So an aspect ratio of 40 for example means that the profile height of the tyre is 40% of its width.
The next two digits represent the size of the wheel rim that the tyre can be fitted to. It is also the diameter of the tyre from bead to bead. So a tyre marked 18 will fit on a 18-inch wheel rim.