A common question is what mm size Amora would be best for you to wear?
Carat is a measure of weight, which is distributed in 3 dimensions.
Thus, you want to normally focus on what the face up mm dimensions are as that is the 'viewable size' rather than the carat weight. (Example - an 8mm round is 2ct, but an 8mm Princess is 3ct...same 'face up size' but the square cuts are usually deeper, and thus weigh more).
To help with this, you can print out this PDF chart of various gem shapes and sizes and then view in person or even cut out the relevant shapes and put on your finger to get a more accurate understanding of what sizes might be the best choice for you!
Here's what it looks like: