How to Read Glasses Frame Size Numbers: Lens Width, Bridge Width & Temple Length Explained

In standard ophthalmic notation:

$$\mathbf{52} \; \square \; \mathbf{18} \quad \mathbf{140} \implies \mathbf{\text{Lens Width (A)}} \; \square \; \mathbf{\text{Bridge Width (DBL)}} \quad \mathbf{\text{Temple Length}}$$

• Lens Width (52 mm): The horizontal diameter of one lens at its widest point. Typically $48-52\ \text{mm}$ (Small/Medium) or $53-56\ \text{mm}$ (Large).
• Bridge Width (18 mm): The shortest distance between the two lenses across your nose bridge. Ranges from $14-16\ \text{mm}$ (Narrow) to $17-21\ \text{mm}$ (Standard to Wide).
• Temple Length (140 mm): The total length of the temple arm from the hinge screw to the very tip behind the ear. Standard sizes are $135, 140, 145,\text{ and } 150\ \text{mm}$.

While the arm prints lens and bridge size, it does NOT print Total Frame Width (the temple-to-temple hinge distance). To calculate approximate total frame width:

$$\text{Total Width} \approx (2 \times \text{Lens Width}) + \text{Bridge Width} + \text{Hinge Endpiece Allowance} (\sim 6-10\ \text{mm})$$

For $52 \ \square \ 18$, total width is roughly $(2 \times 52) + 18 + 8 = 130\ \text{mm}$. If your facial width temple-to-temple is $140\ \text{mm}$, a $130\ \text{mm}$ frame will squeeze your temples, causing pressure marks and headaches.

If your prescription is stronger than $-4.00\ \text{D}$, always choose a frame with a smaller lens width (e.g. 48-50 mm) and a narrow bridge. Because high minus lenses get exponentially thicker at the periphery, shrinking lens diameter by just $4\ \text{mm}$ reduces edge thickness by up to $30\%$ without changing lens index!