Eyeglass frames are sized to fit comfortably on your face, taking into consideration the width of your head, as well as the length from your temple to your ear. Dimensions vary according to brand and style, but the specific frame size is usually printed on the inside left arm of your frames. If these numbers are worn away, you can figure out the size by taking a few measurements.
Place your glasses on a level surface, such as your desk.
Fold the frame arms inward and place the frame on the surface so that the lenses face upward.
Measure across one of the lenses, from the left side to the right side. This is your lens width. Note the measurement in millimeters.
Find the bridge width by measuring from the inside edge of your right lens to the inside edge of your left lens. The bridge width is the space between your lenses that goes across your nose.
Measure the arm length from the very tip of one arm of the frame to the dowel point, where the hinge connects to the frame.
Find the frame width by measuring from one end of the frame to the other, starting and ending where the arms connect to the frame. This measurement isn't part of the standard frame size like the other measurements are, but you might still need it when ordering new eyeglass frames.
The frame size that is printed on the inside left arm of your frames will look something like 52-16-135. The first number is the lens width. The second number is the bridge width. The last is the arm length. All three measurements are given in millimeters.
Although you can get the approximate frame width by multiplying the lens width by two and adding the bridge width, it's a good idea to measure it anyway because it can vary based on the thickness of the rims of the frames and the size of the lugs.