Buying Gemstones for Jewelry: Understanding Gemstone Sizes

For many people, gemstone sizes can be very confusing, not only for those who are unfamiliar with the metric system, but also for those who don't completely understand the exact format in which gemstones sizes are described and provided. The internationally recognized unit of measurement for gems and jewelry, including diamonds, colored stones and jewelry findings is always given in millimeters, usually rounded to the nearest two decimal points.

For our US customers, the following inch to millimeter conversion table may be helpful when buying gems by size for your jewelry needs:

The format used to describe gemstone sizes can also vary depending on the shape of the specific stone. For round gemstones, usually two dimensions are detailed; diameter and depth. For ovals and fancy shapes, gemstones sizes are described using three dimensions; length, width and depth.

Gem buyers should also be aware that gemstones are rarely cut with perfect symmetry, and depending on where a stone is actually measured from, its size may be given as differing values. Thus, it's highly recommended to allow for some variance in regard to exact millimeter sizes when buying colored gemstones for your jewelry settings.

How Big Will My Gemstone Look?

The picture below may be helpful when deciding how big or how small a gemstone you require for your jewelry. This image shows an outline of how a 6.5 mm round stone may look when set in standard ring sizes. A 6.5 mm stone may look large in delicate jewelry designs, but in chunkier designs such as a men's rings, a 6.5 mm stone will appear much smaller than you might expect.

A 6.5 mm gemstone in comparison to standard USA ring sizes (inside diameter).