Looking for the right "size"

Is the gem you are looking for the right "size"?

Many people come to us looking for a certain carat "size" of gem, but they don't realize that often this is not the best measure to tell whether the gem in question will work for their project or not.

Engagement Rings

You (or your client) may dream of just the perfect gem in a ring on the finger, and have an idea of what visual size that gem is expected to be. But how can you best translate that mental image into something that is useful for finding the right size gem? Knowing how to do that is especially useful when shopping online since you can't see the gem in person until it arrives in the mail.

(If the gem isn't the size you expected (or any other issue) we do have a 14 day return policy (read it here), but still it is handy to start with the right parameters to not waste time and energy on gems that just aren't the right size.)

John Dyer custom cut gemstone gif

So, to help you in your search there are some important things to understand. The first is that since carats are a measure of weight (a carat is one fifth of a gram) and not a measurement of visual size they can be misleading. Imagine looking for a one pound block of wood or a one pound block of steel. They both would weigh the same, but the block of wood will LOOK far larger because wood is less "heavy" than steel. In technical terms they have different "specific gravities" and so does each gem material. Diamond is much "heavier" than opal for example. That means a one carat diamond will look much smaller than a one carat opal if they are both cut in the same way.

Depending on the cutting style the depth of a gem can also vary greatly, even when comparing two well cut gems, this means that some have more weight on the bottom of the gem than others and so will look smaller or larger based on the depth even though their carat weight might be similar.

Differing cut depths due to gem cutting style
Notice how different the depths of the gems to the right are. They are both "correct" proportions but different cutting styles.
(Side view shown.)

So when you are choosing a gem it is very important to consider the millimeter size since the varying densities of different gem materials and also the varying depths of different cutting styles can result in a significantly different visual size in gems of similar carat "sizes" (although carat should be called a weight and not a size).

Because of these different factors millimeter (mm) size is far more important for practical purposes than the carat weight since it measures the actual physical size of the gem. You want to know the carat weight because your friends (or customer's friends) will ask. But you need to understand the mm size so you know if a particular gem will work for the design and style you want.

This page is to help you get a better feel for MM sizes and what they mean in visual and practical terms.

When thinking about size also keep in mind the shape of the gem, some shapes will look larger even if they have the "same" mm size. 
See example below
empty ring shanks are a good way to give you the flexibilty to fit a gem into the style of band you like and still save money

Due to differing screen resolutions, etc. this image is probably not actual size. But it serves to illustrate what we are talking about. For actual sizes use the guides below. .

Due to differing screen resolutions, etc. this image is probably not actual size. But it serves to illustrate what we are talking about. For actual sizes use the guides below.

Printable Size Guides
To help you decide about the specific gem or gems you are looking at on our website we offer the PDF documents below that can be downloaded and printed for use in judging visual size.



Download this one for 8.5x11 inch paper (US Document size).
Download this one for A4 paper size.
(Make sure you use the correct paper size.)

If you need a different paper size or want the gem you are interested in placed in the document for printing please contact us via email.


Depth of gem to fit in a ring. Depth
Another important factor to take into account when purchasing a gem is the depth measurement. This will help you know how high the gem will sit in a mounting. If you have a specific setting in mind knowing the depth will tell you whether the gem will fit in it. Info on how we measure the depth is here.

As a general rule the larger the diameter of the gem the deeper it will be in most cases. There are however some cuts which are very shallow relative to their width. (An example  would be some of our "Fantasy" styles, specifically the "Low Profile" category.) But other gems need to be at least somewhat deep to properly reflect light and be beautiful, especially the more traditional flat faceted kinds of cuts.

To understand more about optics, necessary depth and the importance of a good cut watch the video on "Good Vs Bad Gem Cutting" here.


Love our gems but cannot quite afford one right now? 

We can often work out a customized layaway plan for you to allow you to get the gem you want!

Contact us for more details.

Engagement ring gemstones for sale, buy precison cut engagement gemstones in our online catalog

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