How to Measure Diamond Depth?

The beauty of the diamond is what attracts all of us to it. When people see a diamond, its shinning crystal finish and dazzle gives it a very attractive look. If you are familiar with diamonds, you will know that the shine and crystal look of the diamond is largely dependent on the diamond’s depth and table.


While it is easy to see the brilliant shine and the beautiful crystal look of the diamond, it is not easy to know its depth from mere observation. Your diamond depth is as important as its quality because the variation of the depth and table of the diamond in proportion to its size will determine the quality and brilliance of that diamond.

How to Measure Diamond Depth?

When it comes to measuring diamond depth, there are two depth measurements. The first deals with measurement of the actual depth of the diamond, and it’s measured in milimeters. It is the measurement of the height of the diamond, from its culet to the table. This is shown as ‘measurements’ in a grading report.

This image shows exactly how the first measurement is done:

Diamond Table

The second depth measurement is the percentage of the depth. This second measurement of depth is measured in relation to the width of the diamond’s table. As the name implies, it is a percentage and it is measure in relation to 100 percent.

Now here is the pertinent question: ‘How do you measure the depth of your diamond?’

Understanding Diamond Total Depth

There are several methods and instruments made available for measuring a diamond’s depth. Most gemological laboratories that are into measuring diamonds measure the depth using high tech equipment that scans each diamond.
When the diamond is scanned, the equipment takes a minimum of eight measurements of each facet or section of the diamond. After this is done, all of the measurements are added up and then divided to get the average measurement.

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One of the renowned laboratories that participate in this endeavor is the American Gem Society (AGS). This laboratory is preferred to most of the other industries such as GIA because of its manner of operation and calculation accuracy when it comes to measurements of gems and stones.

Decimal pointUnlike other gemological laboratories that round off their results to comfortable decimal points of whole numbers, or half percent or half of a degree as the case may be, AGS has it as one of its key operational policies to give the result with the figure left just as it is, in the very exact way it comes, not minding the number of characters after the decimal or the size of the fraction.

The results are produced from the AGS laboratory in their exact figures. This provides a whole lot of convenience as the results can be easily used and accurately channeled to and for further calculations without running the risk of having distortion in the actual figures and measurements.

How to Estimate Diamond Total Depth?

Estimating the total depth measurement of a diamond that is cut in a round crystal shape can be done using a very simple formula. This formula involves dividing the diamond’s depth figure by the diameter of the average girdle.

What does this mean and how can it be done?

micrometerFirst, you must know be able to measure the actual depth of the diamond. This can be done by making use of a micrometer (like this one)  which will help you get the actual depth of the diamond, that is, measuring from the table of the diamond, down up to its culet.

After that is done, the next step will be to measure the average girdle diameter. This is done by measuring the diamond from one girdle edge to another girdle edge, from the east to west, as well as from the north to the south. These two measurements (horizontal and vertical) are then put together and the sum is divided by two. This will help you know the average girdle diameter of the diamond.

This image shows the different grades of any diamond girdle so you have a better idea how it looks like in real life:

diamond girdle grades

Once these two variables are found out, estimating the total depth is already a done deal using the simple formula mentioned earlier.

What is the Relationship Between Light and Depth?

The depth of a diamond affects and determines the amount of light that will go in through the diamond. At the point when the light enters the diamond, it is the depth (and the Cut of course) of that diamond that will determine the amount of that light that will be retracted and also how much will be reflected.
Remember that the diamond’s light reflection is what accounts for its glitter and its shine.  So you can see why it is important to have sufficient light and correspondingly sufficient reflection coming through the diamond.

It will interest you to know that where a diamond’s depth is very shallow, the light will hit the peak of the facet at an angle that is quite low, and passing through the facet smoothly and conveniently, it will easily escape out through the bottom of the diamond.

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Where on the other hand the depth goes in beyond shallow but is not too deep itself, you will have  a situation where the light enters the diamond from the peak of the facet and hits the second pavilion at, again, a low angle. This will lead to a refraction of the light, which will, in turn, cause an early escape of light out through the bottom of the diamond.

Where the depth of a diamond is ideal, you will have light ray entering the diamond and reflecting at such an angle that it strikes the facets and allows the light to come bright at the top of the diamond, check the below image for a full understanding how light corresponds to different depths.

In essence, you can now understand how getting the depth of a diamond right is essential for a diamond to have that brilliant shine and dazzling sparkle.

Depth Grades

What About Depth and Table?

The table is the flat top of the diamond. Because it is the largest facet of the diamond, it plays a very significant role in the beauty of the diamond.  But the table does not do this alone. It must be matched with an appropriate depth. Being the largest facet of the diamond, the table has a role of retracting light rays entering the diamond and creating a reflection of the same light into the eyes of the observer.

This accounts for the diamond’s brilliance and shine. There is no gain saying that if you want to get your diamond looking great and reflecting light with amazingly dazzling brilliance, you need to pay attention to the depth of the diamond and make sure that it is in consonance and it is compatible with the table of the diamond.

Diamonds are always beautiful to behold. When next you come across a diamond, take some time to admire it and watch out for its features. When you have done that successfully, then you can begin to think of a way to apply these lessons and thus make a good effort at measuring its depth.

The depth and table of the diamond in proportion to its size will determine the quality and brilliance of that diamond.

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