What size glasses frames do I need ?

How to buy the right sized glasses frame.
Glasses frames have numbers usually on the arm
something like this for example 52/16/140

The first measurement is usually the width of each 
eye shape on the front panel of the glasses ie: 52mm (millimeters)

The next measurement is usually the bridge width ie: 16mm

The last measurement is usually the length of the arms ie: 140mm

The depth measurement is not usually marked on the glasses but
is sometimes included on online websites to guide you.
These measurements give and take a little unfortunately, but give you a guide. Hopefully this helps a little.