Buying eyewear online is undeniably convenient—yet sizing uncertainty often holds even the most decisive shoppers back. The good news? Every frame carries a precise code that unlocks the perfect fit. In this guide, we reveal how to decode these numbers and measure your face effortlessly from home.
How to Read the Numbers on Your Glasses (The “Secret Code”)
Take a pair of glasses you already own and look inside the temples or behind the bridge. You’ll notice a sequence of numbers that resembles a cryptic formula.
It typically appears like this: 50 □ 22 150
These three numbers are the identity card of your frame, expressed in millimeters. Let’s decode them, referencing iconic models available on Otticanet.
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Lens Width (e.g. 50):
This is the width of a single lens and the key parameter defining the frame size (S, M, or L). The wrong lens width can make your eyes appear too close together—or too far apart. Consider a timeless icon like the Ray-Ban Original Wayfarer: it’s often available in sizes 50 (standard) or 54 (large). For most face shapes, 50 is the effortless go-to. -
Bridge Width (distance between lenses):
The second number (in this case, 22) indicates the space that rests on your nose. A narrower nose typically requires a smaller bridge (14–18 mm), while a wider nose benefits from 18–22 mm for optimal comfort. Classic optical designs from Persol often feature bridges around 20–22 mm—perfectly balanced and comfortable. -
Temple Length:
The final number (here, 150) measures the length of the arms that rest over your ears, ensuring stability and fit.
From Millimeters to Sizes
We’re used to thinking in standard sizes—Small, Medium, Large—but eyewear introduces millimeters into the equation, which can feel less intuitive.
Here’s your quick conversion:
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Small (S): up to 50 mm — ideal for narrower faces
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Medium (M): 51–54 mm — the most versatile and common fit
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Large (L): 55 mm and above — designed for broader face shapes
Not Sure of Your Size? Try the “Credit Card Trick”
A viral favorite—and surprisingly accurate—the credit card trick helps you determine your face size in under a minute.
It’s not magic, just clever proportion.
How it works:
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Take a credit card (or any similar rigid card).
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Stand in front of a mirror or use your smartphone’s front camera.
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Hold the card vertically, aligning one long edge with the center of your nose.
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Observe where the other edge lands in relation to your eye.
Your results:
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The card extends beyond the outer corner of your eye:
Your face is petite. Opt for Small (S) frames (under 50 mm). Refined, delicate designs—like those from Oliver Peoples—enhance narrower features beautifully. -
The card aligns perfectly with the outer corner of your eye:
You have a balanced, standard face width. Go for Medium (M) frames (51–54 mm). This is the sweet spot—perfect for versatile bestsellers like Tom Ford sunglasses or classic square acetate styles. -
The card stops before reaching the outer corner of your eye:
Your face is broader and more pronounced. Choose Large (L) frames (55 mm+). Bold, oversized silhouettes work best—think geometric designs or the legendary Ray-Ban Aviator in larger calibers (58 or 62).
Final Check: Is the Fit Right?
Stand in front of a mirror and assess the fit:
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Too small if the temples flare outward or your eyes sit too close to the outer edge of the lenses.
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Too large if the frame slides down your nose or touches your cheeks when you smile.
A subtle styling tip: if your optical frames are a size 50, you may find sunglasses in 52 or 54 equally flattering. Designs from Persol or oversized silhouettes by Gucci often wear beautifully in slightly larger sizes.
Now, the only question is: which pair will define your next look?