G-S Round Crystal Size Reference Chart

When replacing an acrylic watch crystal, one of the most important steps is identifying the correct size. G-S round crystals use their own proprietary numbering system, and the listed size numbers do not directly match the actual millimeter measurement. That can make it difficult to compare a crystal package marked with a GS size to the actual opening size of a watch case.

This reference chart helps convert G-S round crystal sizes to their corresponding millimeter measurements. It can be useful when identifying old stock, comparing packaged crystals, or checking measurements before ordering a replacement.

How to Use This Chart

Use the chart below to cross-reference a G-S round crystal number with its approximate millimeter size. This is especially helpful if you have a vintage GS crystal in its original packaging or if you are trying to compare a known GS size to a measured case opening.

Keep in mind that GS sizing is unique to GS. These numbers are not universal crystal measurements, so this chart should be used as a reference rather than a fitment guarantee.

Identify an unknown GS crystal by its marked size
Convert a GS crystal number to millimeters
Compare old parts stock to case measurements
Verify sizing before purchasing a replacement crystal

G-S Round Crystal Size Chart

Click the chart below to open the full-size image in a new tab.

Important Note on Crystal Fit

Size is only one part of proper crystal selection. Even if the millimeter measurement appears correct, actual fit can vary depending on the crystal style, case design, bezel shape, and how the crystal is intended to seat in the watch.

Whenever possible, confirm both the crystal type and the measurement before ordering. A round crystal with the correct diameter may still not fit properly if the profile or fit style is different.

Additional Sizing Guidance

If you are measuring for a replacement crystal, use a caliper to check the case opening as accurately as possible. Then compare that measurement to the appropriate crystal type and fit style. This chart is best used as a conversion reference for GS round crystal numbers rather than as a standalone fitment guide.

For more watch crystal help, browse our other knowledge base articles covering crystal materials, fitment, and sizing terminology.