When you're selecting an elongated diamond (or moissanite, sapphire, or another gemstone), one thing you'll need to consider is the proportion of length to width, which is called the diamond's ratio. While there is an standard range for each diamond shape - more on that later - you also have a lot of freedom to choose the ratio you like best.
When it comes to moissanite or a lab-grown sapphire, choosing your ratio is as easy as selecting the mm length and width you'd like - our handy printable PDF is great for that! But since diamonds are measured by carat weight, not face-up size, visualizing your perfect ratio can be a little trickier.
How to find a diamond's ratio
Diamond certificates will always include the length and width measurements of the stone in millimeters. You can find the ratio by dividing the length by the width. For instance, a 9 x 6.3 mm diamond will have a ratio of 9 / 6.3 = 1.43.
Standard ratios of elongated diamond shapes
Everyone has different preferences for diamond ratios, even within the industry. Here are the standard ratio ranges we select for our clients. I also included some options for more elongated ratios, since our clients sometimes request those. Finding a diamond with a ratio above the top of the elongated range is very rare, and going too far outside the standard ratios can result in less than ideal cut quality.
- Oval diamond ideal ratio: 1.4 - 1.45; for a more elongated ratio, 1.45 - 1.5
- Emerald cut diamond ideal ratio: 1.4 - 1.45; for a more elongated ratio, 1.45 - 1.5
- Marquise diamond ideal ratio: 1.9 - 2; for a more elongated ratio, 2 - 2.1
- Elongated cushion diamond ideal ratio: 1.2 - 1.25
- Radiant cut diamond ideal ratio: 1.4 - 1.45
- Pear cut diamond ideal ratio: 1.55-1.6
The difference between a 1.42 and a 1.43 ratio will be nearly indetectable, so you don't need to worry about that level of precision when choosing a ratio. You'll start noticing the differences more at either end of the range, but even then, the difference is subtle.
A note on lab-grown diamond ratios
Unliked diamond rough that comes from a mine, lab-grown diamond rough crystal is always a rectangle when it comes out of the machine. This means that the resulting diamonds are more uniform in proportion and tend to be more elongated. If you're looking for a mined diamond, you'll find more diamonds under the ranges listed here.
