Online shops sell glasses by three small numbers, and buyers who have never looked inside their own pair do not know what to type. The numbers are the same on every frame: lens width, bridge width and temple length. This calculator reads them back to you, tells you whether the frame is small, medium or large by lens width, and compares the frame front with your face width.
How to use the glasses size calculator
- Find the numbers. Look on the inside of a temple arm of glasses you already wear. They look like 48-19-140.
- Enter the three numbers in millimetres: lens width, bridge width and temple length.
- Enter your face width at the temples. Hold a ruler across the face at temple level and read the width in millimetres.
- Read the results: the size group, the approximate front width, how it compares with your face, and whether the bridge and temple are in the usual range.
Glasses size formula
approximate front width = 2 × lens width + bridge width
fit gap = front width − face width
The measurement definitions, the typical ranges and the lens-width size groups are from EyeBuyDirect’s frame measurement guide, and the advice on frame width against face width is from All About Vision (both retrieved 2026-10-16). The front-width formula is a simple estimate made by this page and ignores rims, hinges and end pieces.
| Measurement | What it is | Typical range |
|---|---|---|
| Lens width (eye size) | Horizontal width of each lens at its widest point | 40 – 60 mm |
| Bridge width | Distance between the two lenses | 14 – 24 mm |
| Temple length | Arm length from the hinge to the tip | 120 – 150 mm (135, 140, 145, 150 common) |
| Lens height | Vertical height of each lens | Not given; matters for bifocals and progressives |
| Size | Lens width |
|---|---|
| Small | 50 mm or less |
| Medium | 51 – 54 mm |
| Large | 55 mm and wider |
Worked example
Your glasses are marked 52-18-140 and your face is 135 mm wide at the temples.
- Lens width 52 mm is in the medium group (51 to 54 mm).
- Bridge 18 mm and temple 140 mm are both inside the typical ranges.
- Approximate front width: 2 × 52 + 18 = 122 mm, which is 13 mm narrower than a 135 mm face. The real frame front is wider than this estimate because of rims and hinges, so measure the front with a tape.
Example frame numbers
| Printed numbers | Lens width | Bridge | Temple | Approx. front width (2 × lens + bridge) | Size |
|---|---|---|---|---|---|
| 46-20-140 | 46 | 20 | 140 | 112 | Small |
| 48-19-140 | 48 | 19 | 140 | 115 | Small |
| 50-18-140 | 50 | 18 | 140 | 118 | Small |
| 52-18-140 | 52 | 18 | 140 | 122 | Medium |
| 54-17-145 | 54 | 17 | 145 | 125 | Medium |
| 56-16-145 | 56 | 16 | 145 | 128 | Large |
Choosing a frame size
- Start from a pair that fits. The numbers inside it are the most reliable starting point.
- Width. Frames should not be narrower than the face at the temples, or they pinch and leave marks.
- Height. Glasses should sit in the middle of the face, no higher than the eyebrows, and progressive lenses need enough lens height.
- Bridge. If glasses slip down the nose, try a narrower bridge; if they pinch, try a wider one.
Optical shops fit frames by eye as well, so treat the result as a starting point. For hats use the Hat Size Calculator, and for earrings see the Earring / Gauge Size Calculator.
Sources
Every figure above comes from these pages, read directly on the date shown. Brand names are used only to identify published guides.
- EyeBuyDirect — Glasses measurements and frame sizes (lens width, bridge, temple; small/medium/large) — retrieved 2026-10-16
- All About Vision — Eyeglass frame size chart and guide (frame width and face width) — retrieved 2026-10-16
Frequently asked questions
What do the numbers inside my glasses mean?
Frames usually have three numbers such as 48-19-140 stamped on the inside of a temple. They are the lens width, the bridge width and the temple length in millimetres, in that order. A fourth number, if present, is the lens height.
What is a typical lens width?
EyeBuyDirect gives 40 to 60 mm as the typical lens width, or eye size. Its size groups are small for 50 mm or less, medium for 51 to 54 mm and large for wider than 55 mm. The page does not say where 54 to 55 mm falls, so this calculator treats 55 mm and up as large.
How wide should my frames be?
All About Vision says the total width of your frames should match the width of your face at the temples, with room at the sides so they do not dig in. EyeBuyDirect advises a frame slightly wider than the face, with no more than a finger width between the temple and the face.
How do I measure frame width?
Run a tape horizontally across the front of the frames, including any hinges or side features. The calculator’s front width, 2 × lens width + bridge, is an approximation that leaves out rims and hinges, so a measured width will be a little larger.
What size bridge and temple do I need?
Bridges typically run from 14 to 24 mm; a smaller bridge suits a narrower nose and a larger one a wider nose. Temples are typically 120 to 150 mm, commonly 135, 140, 145 or 150 mm. The calculator flags numbers outside those ranges. See the Hat Size Calculator for head size.