How to read frame sizes

Look on the inside of one of the temple arms, or on the inside of the bridge. You'll see something like 52□18-145, sometimes written 52-18-145, often next to the model name and colour code.

If the print has worn away, a millimetre ruler will do: measure one lens across its widest point, the gap between the two lenses at the nose, and one arm from the hinge to the tip.

Lens width is the first number: the width of one lens at its widest point. It's also called the eye size.

Bridge is the second: the gap between the lenses, where the frame sits on your nose.

Temple length is the third: the length of the arm, from the hinge to the tip.

The small square means the frame was measured with the boxing system, the international standard (ISO 8624) that draws a rectangle around each lens and measures that. Every listing on this site uses the same system, so the numbers compare directly.

The easiest way to choose a size is to compare with glasses that already fit you. As a rough guide:

• Lens width within about 2 mm of your current pair will usually feel similar. Larger reads wider on the face.
• Bridge is the number to take most seriously. Too wide and the frame slides down; too narrow and it sits high or pinches.
• Temple length is the most forgiving. A few millimetres either way rarely matters.

For the overall width of the front, add the lens width twice and the bridge once, then allow a few millimetres for the hinges at each side.

Lens height is the depth of one lens, top to bottom. It isn't printed on most frames, so we list it on each frame where we have it.

It matters most for progressive and bifocal lenses, which fit distance, middle and reading zones into one lens. Many standard progressive designs ask for a lens height of about 28 mm or more; shorter designs exist. Check with the optician making your lenses before choosing a shallow frame.

Some frames are made for noses with a lower or flatter bridge, with a deeper bridge or longer nose pads so the frame sits off the cheeks and the lenses sit in front of the eyes rather than below them. Where a frame is made this way, its listing says Low bridge fit: Yes.