The three numbers on the inside of a glasses temple, such as 52-18-140, are millimeters: lens width, bridge width and temple length. Add two lenses and the bridge, plus the hinges, and you get the total width of the frame front. For a good fit that total should match your face width at eye level, and your cheekbone measurement is a practical stand-in for it.
If you measured your face for the Face Shape Calculator, you already have that number: it is B, the cheekbone width.
What 52-18-140 means
| Number | What it measures | Typical range |
|---|---|---|
| 52 | Lens width: the horizontal width of each lens opening | 40 to 60 mm |
| 18 | Bridge width: the gap between the two lenses, where the frame sits on your nose | 14 to 24 mm |
| 140 | Temple length: the arm, from the hinge to the tip behind the ear | 120 to 150 mm |
The numbers are usually printed on the inside of one temple arm. A small square symbol sometimes replaces the first dash; it means the lens was measured by the standard box method and does not change the reading. Other characters on the arm are the model and color codes.
Lens widths are often grouped into small (50 mm or less), medium (51 to 54 mm) and large (55 mm or more).
From the three numbers to total frame width
The number that decides how a frame looks on your face is not printed: the total width of the front. You can estimate it.
Total frame width = lens width × 2 + bridge width + the two end pieces
For 52-18-140, the lenses and bridge come to 52 + 52 + 18 = 122 mm. The end pieces, where the front meets the hinges, add a few more millimeters on each side, depending on the design. Thick acetate frames and frames with decorative hinges add more than thin metal ones.
Many online shops list total frame width separately. When they do, use it, because it already includes the end pieces.
How wide should your glasses be?
A frame should be about as wide as your face at the level where it sits: the line through your eyes, just in front of the ears. That is where the arms leave the frame and run back to your ears, and it is the width that tells you whether they will run straight, press in or splay out.
Your cheekbone measurement (B) is taken at the most prominent points just below the outer corners of the eyes, so it sits close to that line. Use it as your target: a total frame width within a few millimeters of B, and not clearly wider. If your forehead is noticeably narrower than your cheekbones, as on a diamond face, aim slightly under B. The measuring guide shows how to take B with a ruler.
The visual effect works both ways. A frame much narrower than your face makes the face around it look wider; a frame much wider than your face makes the face look narrower and the glasses look borrowed.
Lens width and bridge
Within the right total width, the lens and bridge decide where your eyes sit. In a good fit your eyes are roughly centered in each lens horizontally. Lenses that are too wide for the bridge push your eyes toward the inner edges and make them look close-set; too narrow, and the eyes drift toward the outer edges and look wide-set.
The bridge should rest on your nose without a gap above it and without pinching. If frames always slide down, the bridge is too wide for your nose; if they sit high and leave red marks, it is too narrow. People with a low or flat nasal bridge often do better with adjustable nose pads or frames sold as “low bridge fit”, which sit slightly further from the face.
Temple length
Temple length matters less for looks and more for comfort. The arm should run straight back from the hinge, touch the side of your head lightly and curve down behind the ear without pressing. Common lengths are 135, 140, 145 and 150 mm. Too short, and the bend presses on the top of the ear; too long, and the bend sits past the ear, so nothing holds the glasses back and they slide forward.
Use a pair that fits
The most reliable size guide is a pair you already own and like. Read its three numbers and measure the total width of its front with a ruler. A new frame within a couple of millimeters on lens and bridge, with a similar total width, will fit about the same, even in a different shape.
Then check the fit in the mirror: no more than a finger’s width between the arms and your temples, eyes centered in the lenses, frame edges in line with the sides of your face. With size settled, shape and line become the next decision, covered by face shape in glasses for a round face, glasses for a long face and the sunglasses chart. For color, see glasses frame color.