Glasses frame sizes, decoded
Every pair of glasses you've ever owned has its size printed inside the temple arm — three numbers like 52□18-140 — and almost nobody knows how to read them. They're the difference between ordering online with confidence and playing return-shipping roulette. Here's what each number means, how to find yours, and the one measurement that matters more than the others.
- 52□18-140 = lens width 52 mm · bridge 18 mm · temple 140 mm.
- Your size is inside the temple arm of any pair that already fits you.
- Bridge width is the least forgiving number — stay within ±1 mm of what fits.
- Compare frames by total width, not lens width — brands measure differently.
- Measurements predict fit, not looks. For looks, see the frame on your actual face.
The three numbers, explained
All three numbers are millimeters. The □ is just a separator — some brands print 52-18-140.
- Lens width (52) — the horizontal width of one lens at its widest point. Typical range: 47–58 mm.
- Bridge width (18) — the gap between the two lenses, where the frame sits on your nose. Typical range: 16–22 mm.
- Temple length (140) — the arm from hinge to tip. Almost always 135, 140, 145, or 150 mm.
Some frames print a fourth number (lens height) and sunglasses sometimes add a base-curve value, but the three above are the universal standard — you'll find them on a $12 Zenni frame and a $400 Lindberg alike.
What size are you?
If you own glasses that fit: read the numbers off the temple arm. Done — that's your baseline. When shopping, stay within ±2 mm on lens width and ±1 mm on bridge.
If you don't: measure your face width in a mirror — ruler held flat, temple to temple, just below eye level. No ruler? A credit card is exactly 85.6 mm wide, which is roughly the lens-plus-bridge span of a medium frame: hold it centered over one eye — if the card's far edge lands at the center of your nose and the near edge at your temple, you're a medium.
| Size | Face width | Lens | Bridge | Total frame width |
|---|---|---|---|---|
| Small | < 129 mm | 47–49 mm | 16–18 mm | 125–129 mm |
| Medium | 130–139 mm | 50–54 mm | 18–20 mm | 130–139 mm |
| Large | ≥ 140 mm | 55–58 mm | 20–22 mm | 140 mm + |
Compare total width, not lens width. A 52 mm lens in a thick acetate frame can be wider overall than a 54 mm rimless. Total width ≈ (lens × 2) + bridge + rim thickness — most retailers list it as "frame width". That's the number to match to your face.
The bridge is the number that bites
Lens width has wiggle room; temple arms can be adjusted at any optician. The bridge cannot. It's rigid, it carries the frame's weight on your nose, and it's the reason a frame that's "your size" on paper slides down your face all day. Two millimeters too wide and the frame rests on cartilage instead of bone; two too narrow and it pinches.
If you have a lower nose bridge, also look for frames labeled low-bridge fit (larger nose pads, tighter bridge angle, slightly shorter lens height). Mainstream brands increasingly ship both fits of the same model — same style number, different bridge geometry.
Numbers get you the right size — not the right look
Frame measurements answer exactly one question: will it physically fit? They answer nothing about whether it suits you. Two frames stamped 52□18-140 — one round tortoise, one sharp black rectangle — sit identically and look nothing alike on the same face.
So use the numbers as a filter, then judge looks the reliable way:
- Filter by size — your baseline ±2 mm, bridge ±1 mm.
- Filter by shape — our face shape guide narrows the field to styles that flatter your geometry (there's a sunglasses version too).
- See the survivors on your face. A free virtual try-on renders any frame on a 3D scan of you — Frame anchors the render to your measured face proportions, so scale is real, not guessed.
Right size, right shape — verified on your face
Scan once. Import any frame. See true-to-scale renders in seconds.
Download Frame for iOSFrequently Asked Questions
What do the numbers on glasses mean?
The three numbers inside the temple arm — for example 52□18-140 — are millimeter measurements: lens width (52), bridge width (18), and temple length (140). Some frames add a fourth for lens height. The same code appears on nearly every pair of glasses in the world.
How do I find my glasses size without a current pair?
Measure your face temple to temple just below eye level with a ruler in a mirror — or use a credit card (85.6 mm wide, about the lens-plus-bridge span of a medium frame). Under 129 mm face width usually means small, 130–139 mm medium, 140 mm+ large. An AI face scan can measure it automatically.
What glasses size is considered medium?
Roughly lens 50–54 mm, bridge 18–20 mm, temple 140–145 mm — total frame width around 130–139 mm. Brands vary, so compare total width rather than lens width alone.
Can I use my old glasses to find my size?
Yes — if they fit well, the numbers in the temple arm are your baseline. Stay within about ±2 mm on lens width and ±1 mm on bridge. The bridge is the least forgiving number: 2 mm too wide and the frame slides down your nose.
Do frame measurements tell me how glasses will look on me?
Only partially. Measurements predict physical fit, not whether the shape flatters you. Two identically-sized frames can look completely different on the same face. Filter by size first, then judge looks with a virtual try-on or a mirror.