Frame Size Guide: How to Read Your Glasses Measurements
Every pair of glasses carries its size engraved on the inside of one temple arm. Three numbers, in millimetres:
Once you can read that little code — for example 52 □ 20 145 — you know your glasses frame size, and choosing your next pair becomes far easier. This guide explains what each number means, how a well-fitted frame should feel, and how to work out your size from the glasses you already own.
The 3 measurements
All three numbers are in millimetres. The first two describe the front of the frame; the third describes the arms.
Calibre
The horizontal width of one lens at its widest point. It sets how wide the frame sits on your face and is the number that matters most when comparing sizes.
Typically 44–58 mmBridge width
The distance between the two lenses, where the frame rests on your nose. A couple of millimetres here changes everything: too narrow pinches, too wide slides.
Typically 14–24 mmTemple length
The length of each arm, from the hinge to the tip — including the curve that hooks behind your ear. Unlike the first two, it comes in a few standard lengths.
Standards: 135 · 140 · 145 mmSome frames also engrave a model name or a colour code next to the size — you can ignore those for sizing. The small square symbol (□) between the first two numbers is just a separator: it marks the boundary between lens width and bridge.
How your glasses should fit
Numbers are a starting point — comfort is the real test. A well-fitted frame passes these three checks:
The bridge rests, without pressing
The frame should sit on your nose without leaving red marks or digging in — and without sliding down the moment you look at your phone. If you're constantly pushing your glasses back up, the bridge is too wide (or the frame too heavy for its bridge design).
Your eyes sit centred in the lenses
Look in a mirror: each pupil should sit roughly in the middle of its lens, and the frame edges should follow the width of your face — neither squeezing your temples nor floating past them. A quick test: you should be able to slide one finger between the temple arm and the side of your head, but not two.
The temples hook halfway behind the ear
Each arm should run straight along the side of your head, then curve down at about the mid-height of the back of your ear — not on top of it, not far below it. Temples that bend too early push the frame forward; too late, and the glasses slip when you lean over.
If a frame you love fails one of these checks, don't give up on it too quickly — nose pads, temple curvature and pantoscopic tilt can all be adjusted by an optician. That's a five-minute job in store, and at D.Sungkur it's free.
Find your size
The easiest method: take the glasses that already fit you well and read the engraving on the inside of one temple arm. Those three numbers are your reference size — aim for something close (within 2–3 mm on lens width and bridge) rather than an exact match.
No engraving, or glasses long gone? Use lens width as an indicative guide:
| Size | Lens width | Usually suits |
|---|---|---|
| S Small | Below 50 mm | Narrow faces, petite features, many teen fits |
| M Medium | 50–54 mm | Most adult faces — the most common range |
| L Large | Above 54 mm | Wider faces, or a deliberately oversized style |
Keep in mind that two frames with identical numbers can fit differently — lens shape, weight, nose-pad design and temple flex all play a part. The engraving narrows the field; the mirror decides. If you're also unsure about shape, our guide to choosing a frame shape for your face is the natural next read, and our frames & lenses service covers what happens once you've chosen.
Skip the guesswork — try them on
Try-on and professional adjustment are free at our Quatre-Bornes boutique. Bring your current glasses; we'll read your size and fit your next pair precisely.
or call 463 2371 · Newry Complex, St Jean Road, Quatre-Bornes
Frequently Asked Questions
Where do I find my glasses frame size?
Look at the inside of one temple arm of your current glasses. Most frames have three numbers engraved there, for example 52 □ 20 145: lens width (52 mm), bridge width (20 mm) and temple length (145 mm).
What do the numbers 52 20 145 on my glasses mean?
They are millimetre measurements: 52 is the lens width (the horizontal width of one lens), 20 is the bridge (the gap between the two lenses, over your nose), and 145 is the temple length (the arm that rests on your ear). The small square symbol simply separates lens width from bridge.
What frame size am I — small, medium or large?
As a rule of thumb based on lens width: below 50 mm is small, 50–54 mm is medium, and above 54 mm is large. This is indicative only — frame shape, bridge design and materials all change how a frame actually fits, so an in-person try-on remains the most reliable test.
Do two frames with the same size numbers fit the same way?
Not necessarily. Two frames marked 52 □ 20 can sit very differently depending on lens shape, frame weight, nose-pad design and temple flexibility. Use the engraved size as a starting point, then confirm with a try-on — at D.Sungkur in Quatre-Bornes, try-on and professional adjustment are free.
