Glasses and Sunglasses Frame Sizes Explained
All frames are measured in millimetres, with the first larger measurement being the lens size, which will probably be between 48 and 60.
The second smaller measurement is the bridge size, which will be between 16 and 22.
There may be a third measurement around 135mm, which is the total side (also called the temple, or the arm) length.
You may be able to see the size of your existing glasses still printed on the inside of the frame side. You certainly will see it on any ‘new’ frame you might try on.
A typical size would be written 52-16-135, or simply 58x19.
If you choose a frame with a similar size to your existing glasses there should be no problems with the fit of the frame.
Generally speaking the larger the lens size the thicker and heavier the prescription lenses will be, so if you have strong lenses keep this in mind.