There are two ways to measure eyeglasses frame size:
1) Read the tiny lettering on the inside of your glasses. Sometimes the lettering has worn off, or it is too small for you to see even with a magnifying glass. In which case you need to
2) Measure your glasses with a millimeter ruler. The eye size is measured from one side of the lens to the other, horizontally, at the widest points. The bridge size is the distance between the lenses at the closest point. The temple size is measured from the tip to the hinge, including the bend.
Eyeglass frames are measured in Millimeters. The first number is the width of each of the eye openings. The second number is the space for your nose. The last number is the length of the temples- the parts that go back behind your ears. If there is a "B" measurement, that is the vertical height of the lens openings.
Almost all eyeglass frames are designed so they can be adjusted. You can take your eyeglass frames to a local optical professional for an adjustment.
Finding The Right Size Eyeglasses For You
The easiest and fastest way to find the right size glasses for you is to use your current glasses as a benchmark. Once you know the size of your current glasses, you have a frame of reference for a new pair of glasses. Temple size is really not important except is very special cases.