What the Numbers on Glasses Mean & Lens Categories 0-4

Updated: 11 June 2026 · By the Eye-Shop.eu optical team

Look on the inside of the temple of your glasses: you will see something like RB2140 901 52‑18-140. What does it all mean? It is the "identity" of the glasses — model, colour and dimensions — and it helps you buy the right size online with confidence. Here is our opticians' guide:

The 3 size numbers: 52‑18-140

Number	What it is	Typical range
52 (first)	Lens width in mm — the horizontal width of each lens	40-62 mm
18 (after the ☐)	Bridge — the gap between the two lenses (over the nose)	14-24 mm
140 (last)	Temple length — from the hinge to the tip behind the ear	120-150 mm

How to find your size: check the numbers on a pair that already fits you well and look for similar dimensions (±2 mm in lens width). Narrow face → 48-52 mm lens; medium → 52-56 mm; wide → 56+ mm.

Model & colour code

Before the dimensions you will see the model code (e.g. RB2140 = Ray-Ban Original Wayfarer) and the colour code (e.g. 901 = black with a green G-15 lens). With these two codes you identify the product exactly — also useful for checking authenticity: on genuine pairs, the code on the temple always matches the one on the packaging.

Lens categories 0-4: how much light the lens cuts

Under the European standard ISO 12312-1 (CE marking), every sun lens is classified in a category from 0 to 4 according to how much light it absorbs:

Category	Light absorption	Use	Driving?
0	0-19%	Clear/fashion, indoors	✓
1	20-56%	Overcast, light conditions	✓
2	57-81%	Moderate sun, city	✓
3	82-92%	Strong sun, beach — the standard sunglasses category	✓ (daytime)
4	93-97%	High mountain, glaciers, desert	✗ Banned

Most quality sunglasses are category 3 — ideal for a Mediterranean summer. Category 4 is for special use (mountaineering/snow) and is banned for driving because it cuts too much light.

Category ≠ UV protection

Watch the distinction: the category 0-4 measures only the darkness of the lens. Protection from ultraviolet radiation is a separate property — it comes from the UV400 filter. A clear category 0 lens can have full UV400 protection, while a dark "category 3" lens without certification may not protect at all. That is why we always buy from authorised retailers.

Every pair at Eye-Shop.eu lists its full dimensions on each product page and is 100% authentic with certified UV400 protection — so you can pick the right size online, with confidence.