What is a depth percentage – and does it matter?

When it comes to choosing diamonds, most buyers are aware of the 4Cs: cut, colour, clarity and carat weight. They are typically concerned with another C – cost – as well. But what about depth percentage? This is related to the diamond’s cut. What is it? And should it factor into the decision to purchase a diamond?

Introduction to depth percentage

Some experts consider depth percentage to be one of the most important factors in choosing a diamond. But first, what exactly does it mean? The depth percentage is the ratio of the depth of the diamond, as measured from the table (the flat aspect of the diamond on top) to the culet (the tip or bottom of the diamond), compared to the total diameter of the diamond. Let’s consider an example: say that your round diamond has a total diameter of 6.2mm, and the total depth is 4.0mm. The depth percentage is 64.5%, or 4/6.2. What does this mean?

In general, jewellers and other experts assign a ‘quality’ based on the percentage, which are as follows:

• Exceptional or ideal: 58-60%
• Excellent: 60.1-62%
• Good: 62-64%
• Fair: 64-66%
• Poor: Over 66% or under 57%

So, our example diamond is on the low end of good or the mid-range of fair using just this metric. But, when choosing diamonds, buyers should look at a variety of factors and how they interact to affect quality.

Table percentage

One of those other key qualities is table percentage. This is the ratio of the table width compared to the diamond’s total width. Let’s say that the table measures 5.8mm, while the total diameter is 9.5mm. The table percentage is 61%. Here are the ranges for table percentages, according to experts:

• Exceptional or Ideal: 53-58%
• Excellent: 58.1-60%
• Good: 60.1-64%
• Fair: 64-70%
• Poor: Over 70%

Note: These are table percentages for round diamonds. They differ slightly with other cuts. While beliefs vary, some experts believe that a table percentage of up to 75% or even 80% is acceptable for radiant, emerald and princess cuts. A larger table percentage typically increases the size of the diamonds and its brilliance.

Do these percentages matter?

Theoretically, finding the ideal percentages of depth and table should yield a gorgeous diamond. But many experts recommend that buyers choose diamonds that appeal to their eye. While cut, carats, clarity and colour do matter (especially as relates to the monetary value of the diamond), so too does the buyer’s perception and personal taste.

Many people do want a diamond that is beautifully cut with an ideal shape. They want it neither too shallow nor too deep. But often, the naked eye cannot make that determination, and fractions of millimeters in some formula do not make a difference to their enjoyment of the diamond. If buyers are unsure about the percentages and how they relate to appearance and performance, they should seek the advice of a trusted consultant to help them make the best choice.