How are glasses sized

I’m in the market for a new pair of glasses. I’ve seen a couple of realy neat frames online. They appear to have some sort of size code like 32-42-138, in addition to the frame number. Does anyone know what these numbers refer to, or is it just a set of random numbers?

Right on the inside of the nose bridge, at least in my last couple of pair, is a number with a square beside it. Mine currently have “54 ”. This is the size AFAIK.

Since many off-the-shelf glasses are made for smaller people, I’ve learned to look for this when shopping. If I like the frame but they seem small on my face, I’ve learned to ask if there’s a larger size available.

The store should have a book in which they can look-up the style and compare the number on the bridge to the list in the book and let you know if there’s a different size available.

Usually two numbers. Mine are 5219. This is a size in millimeters. First is the width of the lens, second is the depth. The depth can be crucial if you wear bifocals/trifocals - ask your optitian. I imagine the third number might be the entire frame dimension horizontally?

Depth? What the hell is frame depth? The second number is the distance between the lenses in millimeters. The third number is temple arm length.

Maybe frame depth is the width of lens it can accomodate…

The last number (the big one) is the length of the temples.