Measure your eyeglasses’ lens width and lens height, then pick a clip-on that matches or runs slightly larger.
Getting the right clip-on sunglasses starts with two numbers: the width of one lens and its height. Measure those on your existing glasses and you can match them to almost any sizing chart. This guide walks through the process step by step, including how to handle thick frames and printable guides.
What Measurements Do You Need?
You need two core measurements from your prescription glasses: lens width and lens height. Lens width is the horizontal distance across the widest part of one lens. Lens height is the vertical distance at the tallest point, usually near the center.
Some clip-on sellers also account for frame thickness. If your eyeglasses have thick plastic or metal frames, include the outer frame edges around the lens in both measurements. That extra margin helps ensure the clip-on covers the full frame profile.
Step-by-Step: How to Measure
Grab a ruler with millimeter markings and set your glasses on a flat surface, face down. This keeps them steady and makes the numbers easier to read. Then work through these steps:
- Measure one lens horizontally across its widest point for lens width.
- Measure the same lens vertically at its tallest point for lens height.
- For thick frames, extend both measurements to include the frame edges surrounding the lens.
- Compare your numbers to the clip-on seller’s size chart.
- Choose the size that matches or runs slightly larger than your lenses.
VS Eyewear’s clip-on sizing guide confirms all measurements are taken this way and listed in millimeters. Their chart shows common lens sizes ranging from 50 mm x 33 mm up to 60 mm x 45 mm. If your lenses land between sizes, size up — a clip-on that is a bit large still covers fully, while one that is too small leaves part of your prescription lens exposed to sunlight.
Using Printable Sizing Guides
Some brands, including Foster Grant, offer printable sizing guides instead of relying on ruler measurements alone. The key step is printing at 100% scale. Turn off any fit-to-page or scaling options in your printer settings, then verify the printout size before using it.
Foster Grant’s guide includes a built-in nickel reference image for this check. Place a real nickel against the printed image — if they match in size, the guide is accurate and you can lay your glasses directly on it to compare shapes and dimensions.
Printable guides work well because they also help with shape matching. Clip-ons are made for specific frame shape categories like rectangular, round, or aviator. A correct dimension match does not guarantee a fit if the shape profile differs, so holding your glasses up to the printed outline catches both issues at once.
Frame Shape Matching and Fit Rules
Before measuring, identify the frame shape closest to your eyeglasses. Then look for a clip-on designed for that same shape category. A same-size rectangular clip-on will not properly fit round lenses, even if the dimensions look close on paper.
- Size up when in doubt: A clip-on slightly larger than your lenses provides full coverage. One that is smaller leaves edges exposed.
- Watch the fit tolerance:
- Check the seller’s system: Some brands sell by exact millimeter dimensions, others use small/medium/large. Measurements may appear in millimeters, centimeters, or inches depending on the retailer.
Once you have your measurement pairs, comparing options and styles becomes straightforward. If you are ready to shop, our roundup of clip-on sunglasses for prescription glasses covers top-rated models across shape categories.
| Common Lens Size | Clip-On Match |
|---|---|
| 50 mm x 33 mm | Look for 50 mm x 33 mm or slightly larger |
| 52 mm x 35 mm | Look for 52 mm x 35 mm or slightly larger |
| 54 mm x 37 mm | Look for 54 mm x 37 mm or slightly larger |
| 56 mm x 40 mm | Look for 56 mm x 40 mm or slightly larger |
| 58 mm x 42 mm | Look for 58 mm x 42 mm or slightly larger |
Remember that each brand’s chart reflects its own sizing system. A clip-on rated for 54 mm lenses from one company may fit differently than one from another. When in doubt between two sizes, the larger option gives better sun protection. VS Eyewear’s official PDF guide at VS Eyewear’s clip-on measurement guide provides a visual reference for taking both measurements correctly.
FAQs
What if my glasses fall between two clip-on sizes?
Choose the larger option. A clip-on that is a few millimeters bigger still covers the full lens and frame, while a smaller one leaves part of the prescription lens uncovered. Full coverage matters for both sun protection and keeping the clip-on securely attached.
Do I need bridge and temple measurements?
Usually not for clip-ons. Most clip-ons attach by clipping onto the frame itself, so lens width and height are what matter. Some custom makers ask for eyesize and bridge figures, but standard clip-on sizing relies on the two lens dimensions and the frame shape category.
Will clip-ons work on any eyeglass frame?
No. Clip-ons are designed around frame shape categories. A rectangular clip-on needs rectangular glasses, and aviator styles need aviator frames. Dimensions alone do not guarantee a fit when the shape profiles differ, so match both the shape and the measurements.
References & Sources
- VS Eyewear. “How to Measure Your Clip-On.” Official PDF guide showing lens width and height measurement technique.
- Foster Grant. “Fits-Over and Clip-Ons Size Guides.” Printable guide instructions including the nickel print-verification step.
- Foster Grant. “Fits-Over and Clip-Ons Size Guides Product Help.” Brand sizing guidance for clip-on frame coverage.