Glasses Frame Size Calculator

Glasses frame sizing uses a three-number system printed inside every frame. Understanding this system lets you order glasses online with confidence and ensures a comfortable, correctly fitted pair.

The Frame Size System:

[Lens Width] - [Bridge Width] - [Temple Length]

Example: 52-18-140

• 52 = Lens width in mm (width of one lens)
• 18 = Bridge width in mm (distance between lenses, over the nose)
• 140 = Temple length in mm (length of the arm from hinge to tip)

On the frame itself the first two numbers are usually separated by a small square rather than a hyphen, so it reads 52□18 140. That square is the international size symbol and it means nothing beyond “these are millimetres”. Some brands use hyphens, some use a dash and a space. It is the same three numbers in the same order either way.

How to find your ideal size: Check the measurements inside your current glasses frames. These are the most accurate guide to what fits your face.

General face width to lens width guide:

Bridge width: The three bands are 14–17 mm for a narrow or high-bridged nose, 17–19 mm for an average one, and 20–24 mm for a wider or lower-set nose. Eighteen is the single most common number you will see on a shelf. Bridge is the measurement people most often ignore and the one that decides whether the glasses stay put. Too wide and they slide down all day no matter how you bend the arms. Too narrow and they pinch and leave marks.

Temple length:

• 135 mm: Small or narrow faces
• 140 mm: Standard (most common)
• 145–150 mm: Larger or wider heads

Lens Width × 2 + Bridge Width Example: 52 × 2 + 18 = 122 mm across the lenses and bridge.

That figure is not the full width of the frame, and the difference catches people out when they measure a pair against their face. The rims sit outside the lenses, so add roughly 8 to 10 mm for a plastic frame to get the real edge-to-edge width: about 132 mm for that 52-18. Thin metal frames add less, chunky acetate adds more. The calculator shows both numbers, because the first one is what the stamped figures add up to and the second one is what has to fit your head.

Fitting a frame to your face shape:

• Round face → angular, rectangular frames; wider than face adds structure
• Square face → round or oval frames; softens sharp jawline
• Oval face → most shapes work; maintain frame width ≤ widest face point
• Heart-shaped face → bottom-heavy frames (Clubmaster or browline style) balance a wide forehead

Pupillary distance (PD): This separate measurement tells the lab where to centre the optical prescription within each lens, and it is not one of the three numbers stamped on the frame. Most adults fall between 54 and 74 mm, with the average around 63. Every prescription order needs it, so ask your optician for the figure before you buy online.