Frames are often available in more than one size and are usually categorised by the lens width, bridge width and occasionally the arm length. The two most important dimensions are the lens width and bridge width.

These measurements are usually located on the bridge of the frame or occasionally the sidearm. There will be a number for each measurement and they will typically be:

Lens width = 47mm – 56mm

Bridge width = 15mm – 18mm

In most cases they will appear as 55 □ 17

The Lens Width

Imagine if we drew a box around the spectacle lens. Then the horizontal measurement of this box (in mm) would be the lens width.

The Bridge Width

The bridge width is shown on the picture below. This is measured in mm and is fixed on plastic frames. Frames with pads (as below) can be adjusted to fit by moving the pads into alignment with the surface of the nose. This kind of adjustment can easily be achieved at the local opticians for a small fee.

Side Length

This is the full length of the side from its dowel point (where the screw attaches the side to the front) to the tip of the side. The length to bend is the distance from the dowel point to where the side are starts to bend.

The length to bend can be adjusted to fit if the glasses are loose or tight. This is better done at the local opticians who may charge a small fee. If you attempt to do this yourself then you should warm the side with a directional hairdryer and make very small gentle adjustments.

Comparing the style and frame size of your current frames can help give an idea of the best option for your new spectacles.