The first number— the lens size — represents the horizontal width of the lenses. Generally, the eye size of most eyeglass frames ranges from 40 mm to 62 mm.

The second number — the bridge size — is the distance between the lenses. In other words, it's the size of the "bridge" of the frame that rests on your nose. In most cases, the bridge size of eyeglass frames ranges from 14 mm to 24 mm.

The third number — the temple length — is the length of the "stems" of the frame, measured from the frame hinge to the back tip of the temple. Temple lengths generally range from 120 mm to 150 mm.