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Calculating Diamond's Total Depth Percentage

This is a quick "How To" Diamond blog, part of a series of articles that will help you become better at measuring and estimating carat in Diamonds. This method works great for loose or mounted diamonds. (mounted setting might be tricky)

You will need:

  • A Diamond's Average Girdle Diameter (Calculate Here)

  • A Round Diamond or Gemstone to measure

  • Tweezers (for loose diamonds)

  • Millimetre Gauge (Check my recommendations at bottom of the page)

  • Pen and Paper for Notes

  • Calculator or your mobile phone

Once you know the diamond’s average girdle diameter (Check out this Blog if you don't have it), you can determine its total depth percentage in a very simple to use formula.


Measure the diamond from table to culet with a millimetre gauge. Divide this figure by the diamond's average girdle diameter and multiply by 100.

Round your the result to the nearest tenth of a percent.


If the Average Girdle Diameter is 6.00mm and your measurement of Table to Culet is 3.74mm, then

(3.74 ÷ 6.00) x 100

= 0.623 x 100

= 62.3


Here are my recommendations on Tools for measuring Diamonds and Gemstones

My Absolute Favourite is the Presidium Gem Computer Gauge. I can't tell you enough how amazing this tool is, it's top quality.

This pocket computer can do outstanding calculations in a fracture of a second. You can calculate a carat of a Gemstone from the list, using the Specific gravity of the pre-installed Gems, you can also add your own lists. It also comes with a PC software

Maybe for the more serious Gem enthusiasts as it comes at a cost of £327.83 including VAT from HS Walsh (Presidium Gem Computer Gauge (PGCG) - TG75 (

This is a tool that you only buy once in your career.


The other Gauge is more affordable, you can pick them up from ebay at under £10.00


That's it for the Calculating Total Depth Percentage in a Round Brilliant cut Diamond. Thank you so much for reading my blog, keep an eye out for the rest of the "How To" educational blogs

Feel free to share my blog and don't forget to tag me

PS. Please only use my images with permission!


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