If you look on the inside of your glasses, you'll find a number that looks like: 54 [] 17 145. This information shows you the size of your glasses; the lens diameter, the bridge width and the temple (arm) length, all measured in mm.

A: The lens diameter is the width of the lens (in mm), measured from the bridge. Typically, the smaller the diameter, the smaller the size of the frame overall. Diameter measurement for children can range from 39 to 47mm, whereas above that for adults that can go as high as 62mm for oversized frames. It can be a matter of personal choice, but it's also determined by your frame style.

A: The bridge width is the gap above your nose between the lenses. This is usually the middle and lowest number found on the arm of your frame. It's important that this is comfortable - too tight, and the glasses could pinch your nose; too loose and the glasses won't be stable on your face.

A: This is usually the 3rd set of numbers that is measured in millimeters. Typical arm range for kids will be 125mm, 130mm or 135mm in length. Where as adult glasses will range from 135mm all the way to 150mm. The arms should be long enough to sit comfortably over your ears.

• The top of your glasses should be no higher than the line of your eyebrows.
• Getting the right bridge design and position is the key to a comfortable fit.
• The lower edge of the glasses should not sit on your cheeks, so that they don't rub or irritate.
• The size of your glasses should be in proportion to your face. If you have a small face, don't choose large glasses (unless you are trying to make a fashion statement).
• The width of your glasses should not be wider than the overall width of your face at the temples.