Eyewear guide
What the Numbers on Your Glasses Mean
That string of numbers inside the temple arm, like 52□18-140, is your frame’s size. Here’s how to read it and how to use it to shop for a frame that fits.
Where to find the numbers
Look on the inside of one temple arm, the long piece that runs back to your ear. Some frames print the size inside the bridge or on the back of the rim instead. On a well-worn pair the print may have faded, and an optician can measure the frame for you.
You’ll usually see three numbers, such as 52□18-140 or 52-18-140. The small square between the first two means the frame was measured with the boxing system, the standard way frames are sized. All three numbers are in millimeters.
What each number means
- Lens width (52 in the example): The horizontal width of one lens at its widest point. Most adult frames fall between about 40 and 62 mm.
- Bridge width (18): The distance between the two lenses, across the bridge of the frame. Typical bridges run from about 14 to 24 mm.
- Temple length (140): The length of the arm from the hinge to the tip, measured along the bend. Most temples are between about 120 and 150 mm, with 135, 140 and 145 among the most common.
Some frames add a fourth number, the lens height, also called the B measurement. It’s the vertical depth of the lens. You may see it printed after the others or listed on the maker’s website.
Add the lens width twice plus the bridge, and you have a rough idea of the frame’s front width. The real total is a little more, because the hinges and end pieces add a few millimeters on each side.
The other codes on the frame
The rest of the printing identifies the frame rather than sizing it.
- Model name or number: The style of the frame, usually printed on one of the temples.
- Color code: A short code or name, like C1 or a three-digit number, that tells you which color you have. The same model often comes in several colors, each with its own code.
- Brand and origin: Many frames also show the brand name and where they were made.
These details help you or your optician find the same frame again, or the same model in a different size or color.
How to use the numbers when shopping
Start with a pair that fits you well, even an older one, and write down its numbers. Use them as a reference point rather than a hard rule.
- Lens width: Within about 2 mm of your reference pair usually feels similar. Bigger jumps change the overall width noticeably.
- Bridge: This affects how the frame sits on your nose, so stay close to your reference number. One or two millimeters can matter.
- Temple length: If your current temples feel right behind your ears, look for the same length or something within about 5 mm.
- Shape: A 52 mm round lens and a 52 mm rectangular lens look and fit differently, so compare shape as well as size.
These numbers describe the frame, not your prescription. Your eye doctor and optician can tell you which lens options suit your prescription and whether a frame size works well with them.
Get sized in person
Sizes vary a little between makers, and the numbers can’t show how a bridge or nose pad will sit on your face. Trying frames on settles that quickly.
At Aesthetic Eye Care in San Luis Obispo, our eye care team can help you choose frames that best fit the size and shape of your face. Bring your current glasses, and call (805) 439-1010 or request an appointment online.
What does 52-18-140 mean on glasses?
It means each lens is 52 mm wide, the bridge between the lenses is 18 mm, and each temple arm is 140 mm long.
What size glasses do I need?
The easiest way to find out is to read the numbers on a pair that already fits you well and use them as a starting point. If you don’t have one, an optician can size you in person.
Is the bridge number the same as my PD?
No. The bridge number is a frame measurement. Your pupillary distance is a separate measurement taken for your lenses, so ask your optician if you need it.
Are frame sizes the same across brands?
Most makers use the same measuring system, but shape and design mean two frames with matching numbers can still fit differently. Treat the numbers as a guide and try frames on when you can.
Keep reading
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Read about face shapes and framesEyeglass Frame Styles: A Glossary
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Read about frame stylesAccepting new patients
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