Reading 52□18-145: frame measurements that matter

52□18-145 means: 52mm lens width, 18mm bridge width, 145mm temple length. Every frame carries these three numbers on the inside of the temple, and they're the sizing language your factory, your optician, and your customers' opticians all share. The □ is just a separator — a convention from optical labs.

What each number does

Number	Name	Typical range	What it changes
52	Lens width	44–58mm	Overall size on the face; bigger = more fashion-forward
18	Bridge (DBL)	14–24mm	Fit on the nose; low bridges need saddle or keyhole design
145	Temple length	135–155mm	Comfort behind the ear; 145 is the adult default

Sizing a first collection

1. Optical: 49–52□19-145 covers most adult faces. One size is enough for launch.
2. Sunglasses: go 1–2mm wider on the lens (53–55) — sun frames read better slightly oversized.
3. Low-bridge / Asian fit: shorter DBL with a saddle bridge and deeper nose pads carved into the acetate — spec it as a variant of a proven style, not a separate SKU, until demand proves out.

Two things founders get wrong

1. Copying a luxury brand's measurements without its face-fit context — always test a 3D print or sample on real faces.
2. Forgetting that lens width interacts with bridge: 54□16 and 52□18 have nearly the same total width but fit completely different faces.

These three numbers are also the ones you'll see on every technical drawing we send for approval — now you can read them like a manufacturer.