Where to find it
Open your glasses and look at the inside of the temples, the arms that rest over your ears. One of them will show three numbers, often next to the model number and color code, such as 52 19 140. Sometimes a dash or a small square sits between the first two numbers. All three are in millimeters.
What the three numbers mean
| Number | What it measures | Typical range |
|---|---|---|
| 52 Lens width | The width of one lens at its widest point, also called the eye size. | 40–60 mm |
| 19 Bridge width | The gap between the two lenses, where the frame sits on your nose. | 14–24 mm |
| 140 Temple length | The length of each arm, from the hinge to the tip behind your ear. | 120–150 mm |
Use the pair you already own
The most reliable way to choose a size is to start from a pair that already fits you well. Note its three numbers and look for new frames close to them. The lens width and bridge width matter most, because together they decide how wide the frame sits on your face and whether it rests comfortably on your nose.
Temple length is the most forgiving of the three. Many frames come in only one or two temple lengths, and an optician can adjust the tips to fit behind your ears.
Why the same numbers can fit differently
Two frames with identical numbers can still look and feel different. A round lens and a rectangular lens of the same width cover different areas, and a thick acetate front sits differently from a thin metal one. Treat the numbers as a strong starting point, then check the shape and the overall frame width if the store lists it.
When to ask an optician
If you wear a strong prescription, progressive lenses or have a wide or narrow face, a few millimeters can matter more. An optician can measure you in minutes, adjust the fit once your glasses arrive, and tell you whether a frame suits your lenses. An independent optical shop is a good place to start.
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Join the waitlistRelated: How to know your designer frames are the real thing explains the rest of the markings inside the temples.
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