Glasses Frame Size Numbers Explained: 3 Numbers to Check
Three small numbers are stamped inside your temple arm, and they are the most honest sizing advice a frame will ever give you.
Photo by GlassesShop GS / Pexels
Glasses frame size numbers such as 52-18-140 are millimetre measurements. The first is the width of each lens, the second is the bridge between the lenses, and the third is the length of each temple arm. Match them to a pair that already fits you and you can buy almost any frame with confidence.
What do the three numbers on a glasses frame mean?
In a code like 52-18-140, the first number is lens width (the horizontal span of one lens at its widest point), the second is bridge width (the gap over your nose between the two lenses), and the third is temple length (the arm, measured from the hinge to the tip). All three are in millimetres. Lens width and bridge together decide how the front of the frame sits on your face, while temple length decides how the arms rest over your ears. A frame can be wrong in only one of the three and still feel wrong overall: a correct lens width with a bridge that is too narrow pinches, and a correct bridge with arms that are too short pushes the front forward. The numbers work as a set, so read them as one fit profile rather than three separate specs. Many shops also print them with a small square between the first two, like 52□18 140. The square is only a separator.
- Lens width: commonly 40 to 62 mm across adult frames
- Bridge: commonly 14 to 24 mm
- Temple length: commonly 120 to 155 mm, with 135, 140 and 145 mm the usual stock sizes
You will sometimes see a fourth figure, lens height. It is rarely stamped on the frame, but it matters, and we come back to it below.
Shop the frames in this guide
Where do you find the numbers on your current glasses?
Look at the inside of one temple arm, near the hinge. The size code is usually printed or engraved there, often next to a model name and a colour code. If it is not on the arm, check the underside of the bridge or the inner edge of the nose pads. The sequence is almost always lens width, then bridge, then temple length. Colour and model codes are longer and use letters, so ignore them. If the print has worn off, a plain ruler gives you the same information in under a minute. Measure one lens at its widest horizontal point, ideally the inside of the rim. Measure the bridge at its narrowest point between the two lenses. For the temple, lay the arm flat and measure from the hinge pin to the tip, following the bend. Write the three numbers on your phone. That note becomes your reference every time you shop for frames, and it is worth more than any generic size chart.
One small catch: if your frame has thick acetate rims, measure to the lens opening rather than the outer edge, or your lens width will read a few millimetres too large.
What frame size suits your face?
The best frame size is the one whose width roughly matches the width of your face at the temples, with your pupils close to the centre of each lens. As a loose shop convention, lens widths under about 50 mm count as small, 50 to 54 mm as medium, and 55 mm and above as large. Brands do not agree on these cut-offs, so treat them as starting points. The better test is comparison: if your current glasses fit and you like them, stay within 1 to 2 mm of their lens width and bridge, and within 5 mm of the temple length. Going wider than your face makes frames slide and swing outward at the arms. Going narrower squeezes the sides of your head and leaves the lenses sitting too far in front of your pupils, which is where headaches after a long day often start.
| Size band | Lens width | Typical bridge | Typical temple |
|---|---|---|---|
| Small | Under 50 mm | 14 to 18 mm | 135 mm |
| Medium | 50 to 54 mm | 16 to 20 mm | 140 mm |
| Large | 55 mm and above | 18 to 22 mm | 140 to 150 mm |
These are common patterns, not rules. Your own nose shape can move you a couple of millimetres either way on the bridge.
Why does the bridge number cause pinching and slipping?
The bridge number decides how the frame sits on your nose, and it is the figure most people get wrong. A bridge that is too narrow squeezes the sides of your nose and leaves marks. A bridge that is too wide lets the frame sink, so the glasses slide down and the lenses drift away from your pupils. Because bridge width is only a few millimetres, a 2 mm difference is easy to feel. If your glasses slip constantly, check the bridge before blaming the arms. Frames with adjustable silicone nose pads, common on metal and titanium styles, give you a little room to correct this, because the pads can be bent in or out. Moulded acetate bridges cannot be adjusted nearly as much, so for acetate you want the number to be right from the start.
Here is a counterintuitive detail. A frame that pinches at the bridge and slides at the same time is often too narrow overall, not just wrong at the nose. The tight bridge pushes the frame up on the nose sides, and the arms then pull it back down.
Does frame size change how thick your lenses are?
Yes. Larger lens widths mean more lens material, and the edges of a strong prescription grow thicker the further they sit from the optical centre. Two figures matter here: your pupillary distance (PD, typically 54 to 74 mm in adults) and the frame's own centre-to-centre distance, which is lens width plus bridge. A 52-18 frame has a centre distance of 70 mm. If your PD is 62 mm, the lenses must be shifted inward by 8 mm in total, a process called decentration, and the outer edges end up noticeably thicker, especially for minus prescriptions. The closer the frame's centre distance is to your PD, the thinner and lighter your lenses can be.
For strong prescriptions, our advice is to pick a smaller lens width and then consider a higher index. Lensdy offers 1.56, 1.61, 1.67 and 1.74 lenses, and 1.67 or 1.74 in a modest-sized frame makes a visible difference in edge thickness. Ask your optician if you are unsure which index suits your prescription.
- Know your PD before you shop, and compare it to lens width plus bridge
- Strong prescription: lean towards smaller lens widths
- Progressives: keep enough lens height below the pupil for the reading zone, so avoid very shallow frames
How do you use frame size numbers when buying online?
Start with your best-fitting pair, read its three numbers, and look for new frames within 1 to 2 mm of the lens width and bridge, and the same temple length. Then check the product page for the measurements and compare each against your note. This takes a couple of minutes and removes most of the guesswork from buying glasses without trying them on. If the new style has a different shape, such as round instead of rectangular, keep the numbers close but expect it to look smaller or larger than the digits suggest. Round and square frames with the same lens width can feel quite different because height and shape change how much of your face they cover. A tall, large round lens with a 50 mm width can look bigger than a flat rectangular 52 mm one. When in doubt between two sizes, pick the one whose bridge matches yours, since temples can be adjusted at an optician and lens width has more tolerance.
- Read or measure the three numbers on your current glasses.
- Note your PD from your prescription or a measurement you trust.
- Filter for lens widths within 1 to 2 mm of your reference.
- Check bridge and temple length against your note.
- Compare lens height if you wear progressives.
Where can you find frames in your size?
Lensdy stocks more than 200 frame styles, so there is usually a shape in your size whatever your face or prescription. Our prescription glasses collection covers acetate, metal, titanium, rimless and flexible memory-metal frames, with affordable prescription lenses added at checkout. If you like a slim metal look, Gerard - Gold and Shimmer are good places to compare measurements against your own. For something with more presence, try ClarityEdge-Green or PrecisionPeak. Most orders arrive within 1 to 2 weeks, and shipping is free on orders over €59.
Frequently Asked Questions
What does 52-18-140 mean on glasses?
It means a lens width of 52 mm, a bridge of 18 mm, and temple arms of 140 mm. Together these describe the frame's fit. Two frames with the same numbers will sit similarly on your face, even if their styles differ.
Can I use my old glasses' numbers to buy new ones?
Yes, and it is the most reliable method. Stay within 1 to 2 mm on lens width and bridge, and keep the temple length close. Shape still changes the look, but the fit will be familiar.
Is the bridge or the lens width more important?
For comfort, the bridge usually matters more, because it controls pinching and slipping. For appearance, lens width has more effect on how big the frame looks. For the best result, get both close to your reference pair.
Do frame size numbers matter for progressive lenses?
They do. Progressives need enough lens height below the pupil for the corridor and reading area, so very shallow frames can be a poor match. Check the lens height on the product page, and ask your optician if you are unsure.
Your next step
Pick up your current glasses, read the three numbers inside the arm, and save them on your phone. Then browse lensdy.com, filter for frames close to that size, and add the lenses that suit your prescription.