guide to measuring glasses

A Guide to Measuring Glasses and Getting the Perfect Fit

When it comes to buying prescription glasses, the difference between just a few mm could affect the fit and feel of your frames. It could mean that your glasses are too big, too tight or too small, and ultimately they will be uncomfortable and it could ruin your look if they don’t fit the way you need them to. So here’s a guide to measuring glasses with a few tips on how to find the perfect fit for your face.

Use Your Glasses as a Guide

If you have an old pair of frames that already fit you well, these can provide the ideal benchmark. Quite often, your specs will already be able to tell you all the information you need. Most frames – not all – but most modern glasses will display a special code on the inside of the arms or even under the nose bridge. These numbers can be deciphered to help you get the measurements for the lens width, bridge width and full length of the arm.

guide to measuring glasses


The above code seen here from the video for instance, has a code of 50-21-148 and this means that it has a lens width of 50(mm), a bridge width of 21(mm) and an arm length of 148(mm).

Understanding the Measurements

Measuring is one thing but understanding the measurements and how they affect your fit is another. As a general idea, the average lens width is somewhere between 50 to 54; small lenses can be as little as 40 and larger oversized lenses can be as high as 62. Lens width is something that is very much a personal choice but you may find that if you have a bigger head diameter or a wider face, larger lenses are much more flattering and similarly, if you have a smaller head, a more petite lens width will look better.

The bridge width can range from 14 to 24 and this measurement can affect how high or low the glasses rest on your face, the distance the lenses are from your eyes, or how comfortable they fit on your nose. All in all, this measurement can be pretty important. If your specs are too far up on your face or they do not feel comfortable to wear, increasing the bridge distance may be a good idea for you. If the frame sits too low on your face, you may want to decrease the distance.

guide to measuring glasses

The final measurement to understand is the arm length; this is the total length of the arm and together with the shape / bend of the arm, it could affect how well your glasses stay in place, particularly because the arms determine how well they balance on your ears.

Adjusting the Arms

Whilst the lens width and nose bridge measurements can be quite useful for those who are shopping online, quite often with the arms, it can be hard to tell whether they fit you well until they arrive. As a general rule, consider the measurements of your existing specs and try to get the same or similar in size the next time you shop for prescription specs. If you feel like you need to adjust your arms, here’s a super handy video to help you safely alter them at home!


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