Diamond Proportions Guide: Why it Matters More Than Weight

A diamond's light performance is one of the most important factors in determining its beauty and value. The way a diamond interacts with light affects everything from its colour to its clarity.

When light enters a round diamond, it is reflected off the surface and then refracted back through the diamond. This creates a dazzling display of brilliance and fire. The angle at which light passes through the diamond also affects its appearance.

A well-cut diamond will reflect light evenly, creating a uniform sparkle. In contrast, a poorly cut diamond can appear dull and lifeless. The light performance of a diamond is just as important as its physical characteristics, and it is something that should be taken into consideration when shopping for a new stone.

This is why cut grades (officially from a lab only for a round diamond) and a diamond's depth matter in the IGI/GIA certificate. For example, the ideal depth percentage for a round brilliant cut diamond will differ from another diamond's cut and shape. For the same price, you may be able to find a diamond with superior brilliance if it's cut effectively.

The better diamond is sometimes the one with the better table width or width ratio that prevents the diamond from having a dark appearance or undesirable qualities. A diamond's beauty is subjective, but aspects like a thick girdle, a slightly thick culet, star length, pavilion depth, and the table facet can affect how the diamond size appears.

You can have two diamonds of similar carat size but drastically different depth proportions. The table above recommends the best diamond proportions for various fancy shapes and cut grades such as for a round diamond, though other elements like crown angles and pavilion depth may affect your decision.

A diamond's shape and a diamond's facets can affect its light performance. Indeed, you can evaluate the diamond table, pavilion depth, cut grade, girdle thickness, star length, crown height, and diamond depth among other characteristics before simply looking at the carat weight of a cut diamond.

While diamond price plays a role, length to width and cut quality and their interplay with the best proportions should matter, too. Round diamonds are the most popular, and that's why the diamond proportions should be compared with the table above.

A round brilliant diamond may have, for instance, a different pavilion angle, table size, or girdle thickness than another, and that's why jewellers pay attention to different factors during an evaluation, such as crown angles or crown height. A diamond proportions chart helps in this regard, where you can compare round-cut diamonds and other cut diamonds for uniformity.

A diamond's depth affects the ideal diamond proportions as well. Factors like the table facet, which is the largest facet of a diamond, should be considered alongside the diamond's size. Avoid diamonds that have been cut poorly, especially if you can find a similar diamond that reflects light upward and simply presents better. Ultimately, when it comes to light performance, a diamond's brilliance is crucial and will be impacted by cut quality.

The ideal proportions for the crown and pavilion are based on the width of the girdle, which should be 3-3.5% of the total depth of the diamond. Girdle thickness is the width of a gemstone's girdle, which is the band that separates the crown from the pavilion. Generally speaking, the crown proportion compared to the diamond's total depth, also known as the crown height percentage, should be 12.5-17%.