The length of the arms that go over your ears (typically 120–150mm).

Before shopping, look at the inside of your current well-fitting glasses. You will likely see three numbers (e.g., 52 □ 18 140):

Buying eye frames is a balance of medical necessity, physical comfort, and personal style. To get the best results, you need a current prescription and an understanding of how frame geometry interacts with your face. 1. Essential Measurements