You will find the size of your Sunglasses / Optical frame either on the sides of your frame or sometimes it is stamped on the bridge of the frame ( usually VERY SMALL print )

it will be in the form of either 2 numbers separated by a small square box

or 1 number in Millimetres Example :-  136mm for models that have 1 large lens that fits accross the whole frame .

Almost Half of Ray-Bans are only made in one size, If the advertisement through which you are ordering specified ONE SIZE in the drop down box then you will NOT need to know the size as no other size is available in that model.

Sunglasses and optical frame sizes are done in the same way,

All models that have 2 lenses will have 2 measurements for the size

The lens width is the Horizontal width of each lens, it is measured in Millimetres

This is the distance between the two lenses, measured in Millimetres

If the size is 54mm* 19mm

the first number is the lens width 54mm

19mm is the Bridge width

If you measured with a rule accross the total front of the Sunglasses you will find that a model with size 54mm*19mm will have a total width as below

Right Lens 54mm wide , PLUS Bridge width 19mm PLUS Left Lens 54mm wide

Generally Sunglasses have a larger lens width than Optical frames as the lenses have a much larger curve on the lens, so it is not a good idea to buy new sunglasses without trying them on in a local shop first as the actual width between the hinges will rely on the curve of the lens. For Spare Parts you just need to match the size of the model you already have.

Sunglass models with one lens ( Joined in the middle )

These have 1 measurement, this relates to the total width of the sunglasses.