Frame Number Decoder
Type the three numbers printed inside the arm of your glasses. The decoder shows which number is which, draws them to scale, and compares a frame you are considering with a pair that already fits. The numbers describe the frame, not your face, so an optician still confirms the fit.
Your numbers
Look inside one arm of your glasses for something like 52 □ 18 145. Nothing you type leaves this page.
The decoder runs in your browser. It does not ask for photos, your prescription or your name, and it does not save what you type.
Result
Example: 52 □ 18 145
- 52
- Lens width. Width of one lens opening, edge to edge.
- 18
- Bridge. The gap between the two lenses, where the frame sits on your nose.
- 145
- Temple length. The arm, from hinge to tip, including the bend.
What the three numbers mean
All three are in millimeters. The small square between the first two means the lens and bridge were measured with the boxing system; a dash or a space means the same thing.
| Position | Name | What it measures | Typical range |
|---|---|---|---|
| First | Lens width (eye size) | Width of one lens opening, edge to edge | About 40 to 60 mm |
| Second | Bridge | Gap between the two lenses, where the frame rests on your nose | About 14 to 24 mm |
| Third | Temple length | Length of the arm from hinge to tip, including the bend | About 120 to 150 mm |
What the numbers do not tell you
- The full width of the frame front. Lens + bridge + lens gives a rough width across the lenses, but the front extends past the lenses at the hinges. Measure your current front with a ruler, hinge to hinge, if you want a true comparison.
- Lens height. The vertical depth of the lens is rarely printed. It matters for progressive and bifocal lenses, which need room for their reading zone.
- How the bridge sits. A fixed acetate bridge and adjustable nose pads with the same number can rest at different heights on your nose.
- Shape and curve. A round 52 and a rectangular 52 feel different, and a more curved front changes how the frame wraps your face.
- Your face measurements or comfort. The numbers describe the frame. Matching numbers get you close, not all the way.
Bring this to your fitting
- Your current glasses, especially a pair that feels right.
- The three numbers from that pair, and what you like or dislike about how it sits.
- Your prescription, if you are buying lenses with it. See bringing an outside prescription.
An optician checks how a frame sits on your nose and ears, measures where your pupils fall in the lens, and adjusts the frame to you. That is the part numbers cannot do.
Read the full guide to frame sizes, with a worked example comparing two frames.
About this tool
Built by Lens Society to help people read frame sizes before they shop. The ranges and explanations come from our guide to frame sizes, which cites All About Vision and the U.S. Department of Veterans Affairs. The decoder only describes printed numbers; it does not measure your face, check your prescription or recommend a frame. Updated October 24, 2026. Found something wrong? Tell us through the contact page.