By Mohit Patel, Marketing Specialist, Tailor Size Guide
Eyeglasses Size Chart: How to Read Frame Sizes (52-18-140)
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Add Tailor Size Guide as a preferred source on GoogleEyeglasses are sized with three numbers in millimetres, printed on the inside of the arm: for example 52-18-140. The first is the lens width (52 mm), the second is the bridge width between the lenses (18 mm), and the third is the temple length, the arm from hinge to tip (140 mm). Most adult frames fall between 48 and 56 mm lens width, 16 and 21 mm bridge, and 135 and 145 mm temple.
The easiest way to find your size is to look inside a pair of glasses that already fit you well and copy the numbers. If you don't have a pair, this guide shows you how to measure your face, which numbers matter most, and how to choose frames that fit when you can't try them on.
Key takeaways
- Three numbers: lens width - bridge width - temple length, all in mm. Example: 52-18-140.
- Lens width and bridge together set the frame's overall width. They matter most.
- Copy the numbers from glasses that fit, and stay within about ±2 mm on lens and bridge.
- Your pupillary distance (PD) is a separate number your optician needs for the lenses.
- Progressive lenses need enough lens height; check it before ordering.
How to read the numbers on your glasses
Look on the inside of the arm, or sometimes on the inside of the bridge. You'll usually see something like:
52 □ 18 - 140
The little square between the first two numbers comes from the "boxing system," the international method for measuring frames set out in ISO 8624. It means the lens is measured as if it were drawn inside a box. You'll also see the same numbers written as 52-18-140 or 52/18 140. They all mean the same thing.
| Number | What it is | Typical adult range |
|---|---|---|
| 52 (lens width) | Horizontal width of one lens at its widest point | 40 to 62 mm |
| 18 (bridge width) | Gap between the two lenses, where the frame sits on your nose | 14 to 24 mm |
| 140 (temple length) | Length of the arm from the hinge to the tip behind your ear | 120 to 150 mm |
Some frames also list a lens height, the vertical measurement of the lens, which matters for progressive and bifocal lenses. It's usually printed on the brand's website rather than on the frame itself.
Eyeglasses size chart
Brands group frames into rough size categories. The cut-off points vary, but this is how most sizes line up:
| Frame size | Lens width | Bridge | Temple | Typical total frame width |
|---|---|---|---|---|
| Extra small / kids | 40 to 46 mm | 14 to 16 mm | 120 to 130 mm | under about 125 mm |
| Small | 47 to 50 mm | 15 to 18 mm | 130 to 140 mm | about 125 to 130 mm |
| Medium | 50 to 54 mm | 17 to 20 mm | 135 to 145 mm | about 130 to 138 mm |
| Large | 54 to 58 mm | 18 to 21 mm | 140 to 150 mm | about 138 to 145 mm |
| Extra large | 58 mm and up | 20 mm and up | 145 to 150 mm | over about 145 mm |
Total frame width is the full width of the front of the frame, hinge to hinge. It's roughly two lens widths plus the bridge plus a few millimetres for the frame itself. A lot of retailers list it separately, and it's often the single most useful number when you're comparing frames online.
How to find your size
Option 1: copy a pair that fits
This is the most reliable way. Find the numbers on your current glasses and look for new frames within about 2 mm on lens width and bridge width. Temple length matters less; most people can wear anything within about 5 mm of their current pair, and temples can be adjusted by an optician.
If your current pair isn't quite right, adjust from there. Frames slide down your nose? Look for a narrower bridge. They feel tight at your temples? Look for a wider lens or a wider total frame width.
Option 2: measure your face
If you don't have a pair to copy, you can estimate your total frame width by measuring the width of your face:
- Stand in front of a mirror with a ruler held horizontally just under your eyes.
- Measure from the outer edge of your face at the left temple to the outer edge at the right temple, roughly level with your eyes.
- That's close to the total frame width that will look balanced on you.
A face width of about 130 mm suggests a medium frame. Under about 125 mm suggests small, over about 140 mm suggests large. Our guide on how to measure your face for sunglasses works the same way for glasses.
Option 3: use a credit card
A standard credit card is about 85.6 mm wide. Hold one edge at the centre of your nose, below your eyebrows, and look in a mirror. If the far edge of the card reaches the outer corner of your eye, you probably suit a medium frame. If it goes past, a small frame. If it falls short, a large frame. It's rough, but it's surprisingly useful.
How glasses should fit
Once you have a pair on, check these:
- Your eyes sit near the centre of each lens, horizontally. If they sit noticeably towards the inside, the frame is too wide.
- The frame isn't wider than your face at the temples. A little wider is fine; a lot wider looks oversized and slides around.
- The arms don't press on your temples. If they leave marks, the frame is too narrow.
- The bridge sits flat on your nose with no gap and no pinching.
- The arms reach just past the tops of your ears and curve down behind them without digging in.
- The glasses don't slide down when you look down or nod.
Small problems with the arms and nose pads can usually be fixed by an optician adjusting the frame. Problems with the lens width or overall frame width can't.
Bridge fit and low-bridge frames
The bridge is where a lot of fit problems start. If your nose bridge is low or flat, or your cheekbones are high, standard frames often slide down or rest on your cheeks. Many brands now make low-bridge fit frames, sometimes called "Asian fit" or "alternative fit," with taller nose pads that lift the frame away from the cheeks. If you've always had glasses that touch your cheeks when you smile, look for that option.
Frames with adjustable nose pads (small pads on metal arms) are more forgiving than frames with a moulded bridge, because an optician can move the pads to fit your nose.
Pupillary distance (PD)
PD isn't part of the frame size, but you'll need it to order prescription glasses online. It's the distance between the centres of your pupils, and it tells the lab where to put the optical centre of each lens. Most adults have a PD somewhere between about 54 and 74 mm, with an average around 63 mm.
Your PD is often written on your prescription. If it isn't, ask your optician, or measure it:
- Stand about 20 cm from a mirror and hold a millimetre ruler against your brow.
- Close your right eye and line up the zero with the centre of your left pupil.
- Close your left eye, open your right, and read the mark at the centre of your right pupil.
- Repeat a few times and use the average.
A PD measured by an optician is more accurate, especially for strong prescriptions and progressive lenses.
Lens height and progressives
If you wear progressive or bifocal lenses, check the lens height before you choose a frame. Progressive lenses need enough vertical room to fit the distance, middle and reading zones. Many progressive designs need a lens at least around 28 to 30 mm tall, though your optician will know the minimum for your specific lens. Very narrow, rectangular frames can be too short.
Frame shape and face shape
Fit comes first, but shape is what makes you like what you see in the mirror. A few common pairings:
| Face shape | Frames that often suit it |
|---|---|
| Round | Rectangular, square, angular frames that add definition |
| Square | Round, oval or softer frames that balance strong angles |
| Oval | Most shapes; wider frames keep proportions balanced |
| Heart | Frames wider at the bottom, light or rimless tops |
| Long / oblong | Deeper frames with more height, decorative temples |
These are suggestions, not rules. Our guide to the best glasses by face shape has photos and more detail.
Sunglasses and reading glasses
Sunglasses use exactly the same three numbers, so everything here applies. They tend to run larger, often 55 to 62 mm lens width, because bigger lenses block more light. Our sunglasses size chart and the explainer on what the numbers on sunglasses mean cover them in detail.
Ready-made reading glasses are usually sold in one or two sizes and often don't list numbers at all. If they keep sliding down your nose or pinching, a pair made to your measurements will be far more comfortable.
Children's frames
Children's glasses use the same system, with lens widths often between about 38 and 48 mm and shorter temples. Kids grow fast, so check the fit every six months or so. Signs a child has outgrown their frames include the arms not reaching behind the ears, red marks on the sides of the head, and the frame sitting high above the eyebrows.
If you sell eyewear online
Fit is the biggest reason glasses come back, because shoppers can't try frames on. On each product page:
- Show lens width, bridge, temple, lens height and total frame width.
- Group frames into small, medium and large with the millimetre ranges.
- Explain how to find the numbers on a pair the shopper already owns.
- Say whether a frame is available in low-bridge fit.
Our size guide for eyeglass frames covers how to set up a frame size chart, and Tailor Size Guide can add it to every product page.
Frequently asked questions
What do the 3 numbers on eyeglasses mean?
They're lens width, bridge width and temple length in millimetres. In 52-18-140, the lens is 52 mm wide, the bridge is 18 mm, and the arms are 140 mm long.
What is a medium frame size for glasses?
Medium frames usually have a lens width of about 50 to 54 mm, a bridge of 17 to 20 mm, and a total frame width of about 130 to 138 mm.
How do I know my glasses size without old glasses?
Measure your face width at temple level with a ruler in front of a mirror. About 130 mm suggests a medium frame. Under about 125 mm suggests small, and over about 140 mm suggests large.
Does temple length matter?
Less than lens and bridge width. Most people can wear temples within about 5 mm of their current pair, and an optician can adjust how they curve behind the ears.
Is pupillary distance the same as frame size?
No. PD is the distance between the centres of your pupils, used to position the lenses. Frame size describes the frame. You need both to order prescription glasses online.
What size glasses for progressive lenses?
Choose a frame with enough lens height for progressive lenses. Many designs need about 28 to 30 mm or more, but ask your optician for the minimum for your lens.
Sources and standards
- ISO 8624, Ophthalmic optics: Spectacle frames, measuring system and terminologyDefines the boxing system used to measure lens width and bridge width on frames.
- Dodgson NA (2004), Variation and extrema of human interpupillary distance, Proc. SPIE 5291A widely cited study of adult pupillary distance, with an average around 63 mm and most adults in the mid-50s to mid-70s mm.
- ISO/IEC 7810, Identification cards: Physical characteristicsSets the standard bank card width of 85.60 mm used in the credit card method above.
- Tailor Size Guide sunglasses size chartOur reference chart for frame measurements, used across the eyewear pages on this site.
Selling eyewear on Shopify?
Show lens, bridge, temple and total width on every frame so shoppers can compare with the pair they own. Tailor Size Guide adds per-product size charts with no theme code.