What is depth percentage in a diamond?
By Jared James · Last updated 21 May 2026
Definition
Depth percentage is the measurement of a gemstone's depth, from the table on top to the culet at the bottom, expressed as a percentage of its diameter. So a round diamond that is 6.5 mm wide and 4 mm deep has a depth percentage of about 61.5%, which sits in the ideal range for a round brilliant. This ratio is one of the key proportions gemologists use when assessing cut quality, because a stone cut too shallow or too deep sends light escaping sideways rather than bouncing it back up through the top.
Frequently asked questions
- What is the ideal depth percentage for a round brilliant diamond?
- For a round brilliant, an ideal depth percentage generally falls between 59% and 62.5%. Stones in that range tend to reflect light well and look lively; outside those limits, you risk a stone that looks dark in the centre or glassy.
- Does depth percentage matter for fancy shapes?
- Yes, though the ideal ranges differ by shape. An oval diamond, for example, typically performs well in a slightly different range than a round, so it is worth checking the recommended proportions for whichever shape you are considering.
- Where do I find a diamond's depth percentage?
- It is listed on any reputable grading report, including those from GIA and IGI, under the proportions or measurements section alongside table percentage, crown angle and other key figures.
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