Your Simple Guide to Glasses Sizes

Unlike shoe size or waist size, there’s no universal sizing for glasses.
Every frame has its own shape and fit — which can make choosing a bit confusing!
So here’s a super simple way to understand how glasses sizing works.

1️⃣ Sizing by Numbers on the Frame

If you ever look closely inside one of the arms (the bits that go behind your ears), you’ll often see a few numbers like this:
50 – 20 – 145

These numbers give you clues about the size of your glasses:

50 = the width of one lens (in millimetres)

20 = the bridge (the gap that sits on your nose)

145 = the length of the arm (called the temple)

Lens Width Size Guide (mm)

Small = 46-50

Medium = 50-54

Large = 54+

Bridge Width Size Guide (mm)

Small = 15-17

Medium = 18-20

Large = 20+

Temple Width Size Guide (mm)

Small = 135

Medium = 140-145

Large = 145+

2️⃣ Sizing by Total Width (The Simple Way)

This is the easiest and most helpful way to know how glasses will fit.
It’s the total width across the front of the frame, from one hinge to the other — basically how wide the glasses sit on your face.

Small = 130mm or less

Medium = 130 to 140mm

Large = 140mm+

3️⃣ The Credit Card Trick (Quick and Clever!)

No ruler? No problem.
A credit or debit card is roughly the same width as a medium-sized lens — so you can use it to guess your size.

Here’s how:

  1. Stand in front of a mirror.

  2. Hold the card vertically against your nose (so one edge touches the centre of your nose).

  3. Look where the other edge ends:

    • Lines up with the corner of your eye → you’re a Medium

    • Goes past the edge of your eye → you’re a Small

    • Stops short of the edge of your eye → you’re a Large

It’s a quick, easy way to estimate your size — not perfect, but surprisingly accurate!

Need a Hand?

If you’re still unsure, don’t worry — we help people find their perfect fit every day.
Visit us in Loftus or Skelton for a personal fitting and expert advice.