Eyeglass frames are broadly divided into 3 size categories- Small, Medium & Large. To determine what fits you, either keep your prescriptions handy or look on the insides your old frame temples for the exact numeric size specifications.
Frame size is a combination of numeric values usually represented in sets e.g. 53-18-140 known as the eye size, bridge size & temple size respectively.
Horizontal width of frame’s lens measured in millimeters.
Distance between two lenses measured in millimeters.
Length of the entire single temple