Tips and Tricks

Round Brilliant MM to Ct Guide by Rare Carat

Although carats are standard measurements for diamonds, most people don’t know how to relate that to measurements they know. Using MM is a great way to do just that. Carats are a specialized unit of measurement, and if you’re not handling diamonds and gems all day long, then chances are you’re not familiar with their size. For instance, if I told you I had a one carat diamond, how big is that? The size of a quarter? Or maybe the size of a Skittle? Millimeters can prove quite useful when comparing diamond sizes. This guide and a mm ruler will be your best diamond buying friend.

What to Know Before Using a Millimeter Guide

Before I start listing carat to mm comparisons, there are a few important points to note. This guide is only helpful for comparing the size of round brilliant cut diamonds, using this guide for any other cut will give you inaccurate results. Additionally, this info is based on excellent cut diamonds. Excellent is a diamond cut grade that is given to stones that are as proportionally perfect as possible. (Say that five times fast.)

MM to Ct Conversions For Round Brilliant Diamonds


If you have any questions about how to use this guide or about diamond sizing in general, don’t hesitate to reach out to our gemologists via the chat bubble in the bottom right hand corner. Our professional gemologists are at the ready!

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