The Eyewear Frame Sizing Guide: What 48-20-145 Means & How to Get the Right Fit
Every pair of quality prescription glasses or sunglasses carries three numbers stamped along the inner temple arm, usually separated by a small square: something like 48 □ 20 - 145.
These aren’t serial numbers or batch codes. They represent the foundational dimensions of the frame in millimeters—specifically the lens width, bridge distance, and temple arm length.
However, two frames with the exact same “48-20-145” stamp can fit completely differently on your face. A chunky acetate frame and an ultralight wire frame might share identical lens numbers, but one will feel roomy while the other squeezes your temples.
Here is a breakdown of what each dimension actually measures, why total frame width is often the deciding factor, and how to choose the right proportions for your face or brand collection.