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Diamond proportion is the ratio and size of the diamond’s depth, width and table. The exact proportions like table and depth percentage play a huge role in the beauty of a diamond. Diamond proportion is an element of Diamond Cut and is critical to a stone’s brilliance and value.
With ideal diamond proportions, a diamond takes in and reflects light well—causing brilliance and fire. This 1.26 carat round cut diamond is a stunning example of a diamond with ideal cut proportions.
If a diamond is cut too shallow or too deep, light is lost out the sides and doesn’t reflect as well back to the eye. In other words, if a diamond’s proportions are poor, the diamond looks dull and lifeless.
Because a diamond with ideal cut proportions offers more brilliance, the price also tends to be higher for these diamonds. Throughout our years of experience, we find that the higher price is worth it, because cut quality impacts the diamond’s beauty more than any other feature. That’s why we suggest spending a good amount of your engagement ring budget on Cut quality, over other features like Color and Clarity.
Diamond proportion is calculated using the dimensions of the table size, crown height and pavilion depth in relation to the diamond’s diameter. Each calculation describes the angles and ratios of the diamond’s precise cut. These aspects are universally measured in millimeters (mm) and/or percentages. The formulas for each specific component of a diamond’s proportions are listed below.
Table percentage is calculated by dividing the table width (top surface area) by the diameter. For example, if the table facet is 3mm wide and the diameter is 5mm, the table percentage is 60%.
Width is calculated by measuring from one end of the girdle (the diameter at its widest point) to the opposite end of the girdle.
Depth percentage is calculated by dividing the depth of the diamond (its height) by its width. For example, if a diamond measures 3mm in depth and 4mm in width, the depth percentage is 75%.
The table, depth and width all combine to impact how well a diamond refracts and reflects light. That’s why it’s essential to find a diamond with ideal cut proportions in each area.
There are several factors that impact a diamond’s proportions, including the table size and total depth. How well a diamond interacts with light is affected by the size, shape and angle of each facet.
Here are the 10 main components that impact diamond proportion:
The best diamond proportions allow light to refract and reflect back to your eyes. The ideal round diamond proportions are listed in the table below and based on expert recommendations.
|Best Diamond Proportions for Round Brilliant Diamonds<|
|Depth Percentage||59 to 62.6%|
|Table Percantage||54 to 57%|
|Girdle Thickness||Thin to Slightly Thick|
|Culet||None to Pointed|
|Length to Width Ratio||1.0 to 1.03|
Each of these factors plays a role in the beauty and brilliance of the diamond. By staying within these ideal diamond proportions, you’ll end up with a stunning diamond that captures and reflects light. For example, this 1.32 carat round diamond is exceptionally brilliant because it’s well-proportioned.
To find the best proportions, start by looking at GIA and AGS graded Excellent and Ideal cut diamonds. Narrow down your search to the recommendations above, as some Excellent and Ideal cut diamonds won’t meet these ranges.
For help reviewing a specific diamond’s proportions, reach out to our experts.
Ideal diamond proportions depend on the shape, as each one interacts with light differently. As you look at diamonds, be sure you’re getting the best diamond proportions for the shape. To find these proportions, look at Excellent and Ideal cut diamonds, but remember that not all of them will meet the recommendations below.
Best Diamond Proportions for Every Diamond Shape
|Shape||Depth %||Table %||Girdle||Culet||L to W Ratio|
|Round Brilliant Cut||59 – 62.6%||54 – 57%||Thin-Slightly Thick||None-Pointed||1.0 – 1.03|
|Princess Cut||68 – 74%||69 – 75%||Thin-Slightly Thick||None-Pointed||1.0 – 1.04|
|Cushion Cut||61 – 68%||< 68%||Thin-Slightly Thick||None-Pointed|
1.0 – 1.08 (sq)
1.15 – 1.25 (rect)
|Emerald Cut||61 – 68%||61 – 69%||Thin-Slightly Thick||None-Pointed|
1.30 – 1.45
|Asscher Cut||61 – 68%||61 – 69%||Thin-Slightly Thick||None-Pointed||1.0 – 1.05|
|Oval Cut||< 63%||53 – 63%||Thin-Slightly Thick||None-Pointed||1.30 – 1.50|
|Pear Shape||< 68%||53 – 65%||Thin-Slightly Thick||None-Pointed||1.45 – 1.75|
|Radiant Cut||< 67%||61 – 69%||Thin-Slightly Thick||None-Pointed|
1.0 – 1.05 (sq)
1.20 – 1.50 (rect)
|Heart Shape||56 – 66%||56 – 62%||Thin-Slightly Thick||None-Pointed||1.0 (or as close as possible)|
|Marquise Cut||58 – 62%||53 to 63%||Thin-Slightly Thick||None-Pointed||1.85 – 2.1|
By staying within the recommended diamond proportions, you’ll narrow down your selection of diamonds to the very best. You’ll knock out diamonds that will look dull and lifeless in an engagement ring.
Cut quality, including diamond proportions, is the most important factor in a diamond’s appearance. You’ll still want to pay attention to the other of the 4Cs: Color, Clarity and Carat.For help in choosing the right diamond, use the HD imagery on James Allen’s or Blue Nile’s websites, or reach out to our experts. We’ll take a look at the diamond you’re considering and make sure it gives you the most beauty for your budget.
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