The short answer: the three numbers printed inside your glasses arm — like 52–18–145 — are the lens width, bridge width, and temple (arm) length, all in millimeters. Find these on a pair that already fits, match them within a millimeter or two, and buying online stops being a gamble.
What each number means
| Number | Measures | Typical range |
|---|---|---|
| 1st — Lens width | Width of one lens, side to side | 46–58 mm |
| 2nd — Bridge width | Gap between the two lenses (over your nose) | 14–24 mm |
| 3rd — Temple length | Length of the arm, hinge to tip | 135–150 mm |
So 52–18–145 means 52 mm lenses, an 18 mm bridge, and 145 mm arms. Some frames also list a fourth number — lens height — and occasionally the total frame width.
Where to find the numbers
Look on the inside of the temple arm (the part behind your ear), or sometimes on the bridge. They are printed small, often as 52▢18 — the little square is the industry symbol for the bridge measurement.
How to find your size without an optician
- Grab a pair of glasses that already fit you well.
- Read the numbers off the arm.
- Shop for frames within about 2 mm of your lens width and bridge — the two that matter most for fit.
- No frames to measure? A US adult medium is roughly a 50–52 lens width; narrower faces 46–49, wider faces 54–58.
Which number matters most
- Lens width + bridge decide whether the frame sits right on your face — get these closest.
- Total width (lens + bridge + lens) should be near the width of your face; frames much wider slide, much narrower pinch.
- Temple length is forgiving — most arms bend to fit, so within 5 mm is fine.
From our test bench. Sizing is the number-one reason a frame looks wrong on the right face. We list the full measurements on every product for exactly this reason — and pair them with the Frame Finder so shape and size are both handled before you buy.
FAQ
What if my glasses do not have numbers printed?
Measure the lens width with a ruler across one lens at its widest point, and the bridge as the gap between lenses. Compare those millimeters to product listings.
Is a bigger lens width always more comfortable?
No — comfort comes from matching your face width and bridge, not from bigger lenses. Too-wide frames slide down and sit crooked; the right width stays put.
Part of How to Choose Glasses Frames · Try the Frame Finder · Last updated: July 20, 2026
