What 49□18-146 on a frame means
The inside of every temple carries the model name and three numbers in small print. On the Farris TJ2158 from our post they read 49□18-146. These numbers tell you in advance how a frame will sit on your face.
The first number, lens width
49 is the width of one lens in millimetres. A bigger number means a wider lens and a larger frame. Most sit between 46 and 56.
The box and the second number, bridge
The □ sign means the size uses the boxing system. 18 is the width of the bridge between the lenses. If glasses pinch your nose or slide down, the bridge is often why.
The third number, temple length
146 is the length of the temple in millimetres. A short temple presses behind the ear, a long one lets the glasses slide forward.
What the temple does not say
Our post gives two more sizes. The full frame width is 135 mm and the lens height is 46 mm. Height matters most for progressive lenses, because the distance and near zones have to fit inside it.
Start from your old glasses
If your old glasses fit well, send us the numbers from their temple. A couple of millimetres make no difference, 5 mm or more is a different size. Trying them on in the shop is still the surest way.