Most sunglasses list three key numbers in millimeters (e.g., 52-18-140) on the inside of the temple arm: Sunglasses and Eyeglasses Size Guide - Mia Burton
: The card edge aligns exactly with the outer corner of your eye.
: Stand in front of a mirror and place the short edge of the card against the center of your nose.
: The card edge ends before reaching the outer corner of your eye. Understanding Sunglasses Measurements
To buy sunglasses by size, you can use a common household item like a credit card (or any standard-sized paper card) as a quick reference tool. Because a standard card is roughly the width of a "Standard" lens (54mm), it acts as a reliable benchmark for finding your frame category.
: The card edge extends past the outer corner of your eye.
