Glasses Frames -Our Frame Sizing Information

By Steve Mower, Owner/Optician - March 12, 2026

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Glasses Frames: How to choose the right-sized eyeglass frames.

When shopping for glasses frames, whether for prescription or non-prescription, it is really important that you choose one that fits properly. Ideally, the glasses frames should be wide enough so that the temples, or 'arms,' go straight back to your ears without putting pressure on the side of your head. That pressure can result in headaches and unsightly dents in your head, and nobody that I know wants dents in their head. Glasses frames should also not be so wide that they slide down your nose all the time.

2. Optical Frame Size and Bridge Width - This is the way prescription eyeglass frames are sized. All prescription frames are sized based on 3 measurements, in millimeters:

1. The length or width horizontally, of one lens in millimeters (mm).
2. The length or width of the bridge, again, in millimeters (mm).
3. The length of the temples in millimeters (mm).
4. The lens height in millimeters (mm).

A Chart-

So a typical size might look like "53-18-138" (lens-bridge-temple, usually printed on the inside of the temple) This information is important to opticians, but because of the widely different frame styles available, these numbers are fairly meaningless to most eyeglass shoppers. However, knowing what these numbers represent can help you to understand exactly what you are getting, especially in combination with the frame fit. When available, we also provide the lens height. The height, or depth as you may, is the mm measurement from top to bottom of the lens and is not critical for sizing but is important when buying progressive lenses.

Conversion to inches. One millimeter is .03937 inches. You can roughly calculate the total width of your current eyeglasses in inches. See above image.

First determine the total width in millimeters... Eye Size x 2 + Bridge Width +~ 8-10mm end-piece extension. (Most frames have temples that extend away from the frame front. It varies.)

Frame "Fit" - We group our eyeglass frames into Frame-Fit categories. A Medium Fit fits medium width faces. 

Small		44-47mm
Small Medium		47-50mm
Medium	.......	49-52mm
Medium Large		52-54mm
Large		54-56mm
Extra Large		56mm and up

*This is a rough guide. The thing is that the extension of the temples and the bridge width can make a big difference in the "fit". A 46-22 can fit the same as a 48-18. Both are 114mm across.

TIPS:

1. You can filter your search on our site by Frame Fit, Bridge Width, and Temple Length. Choose a frame fit/eye-size and then choose a bridge width and then temple length.
2. Frames with adjustable nose pads provide the freedom to have the pads adjusted to fit, whereas frames without adjustable nose pads will fit or not.
3. You do not have to be accurate to the millimeter. 1 millimeter difference either way in the eye-size, bridge, and temple isn't enough of a difference.
4. Quality eyeglass frames are adjustable. Opticians can fit the frame to your face properly.   
5. The best way to determine the frame size you need is to pick a frame that you own, or have tried on that is comfortable for you. Read the numbers on the inside of the temples and search accordingly.

Here are 2 handy conversion calculators...

Millimeters to inches-

Convert mm to in

 

www.metric-conversions.org

 

And inches to millimeters-

in to mm calculator

 

www.metric-conversions.org

 

 

About the Author Steve Mower is a seasoned eyewear specialist with over 38 years of experience in frame materials and vision care. He combines deep technical knowledge with a passion for helping people find the perfect eyewear. Throughout his career, Steve has worked closely with manufacturers, designers, and eye care professionals to understand the nuances of frame materials, durability, and comfort. This expertise ensures that the information provided here is both accurate and practical for consumers seeking reliable guidance. Steve is committed to transparency and quality, regularly updating content to reflect the latest industry standards and innovations in eyewear technology. Steve is a licensed dispensing optician and creator of Mojo BluBlock Tints and owner of Reading Glasses Etc. He has been an optical retail manager and has consulted on progressive lens development. Steve has been offering unique reading glasses solutions online since 2010. Steve is a member of the Opticians Association of Virginia and the Opticians Association of America.  For more insights and professional advice, contact via e-mail at steve@readingglassesetc.com.