Measuring Diamond's Table 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 settings might be a little tricky)

You will need:

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

  • A Round Diamond or Gemstone to measure

  • Tweezers (for loose diamonds)

  • Table 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 table percentage in several methods. The most accurate one is the Direct Measurement


Direct Measurement


The direct table measurement method is very accurate for mounted and loose diamonds. To measure the table, first, you will need a table gauge. (Not many of them around, I found mine on the GIA Store)

It’s easier if you can position the Diamond on a stone holder or something with a V shape to sink the pavilion, so the Diamond sits flush. Press the table gauge against Diamond’s table to keep the stone as steady as possible.


Measure the table facet from the corner to the opposite corner. A round brilliant Diamond has eight table corners, so you have to measure it in four directions.

Measure the four measurements to the nearest five-hundredths of a millimetre and divide the total by four to find the average.

This is the number you use to calculate Diamond’s table percentage.

For an Example:

If the four table measurements are 3.00, 3.05, 3.05, and 3.00, then

The Average Table Diameter equals to (3.00 + 3.05 + 3.05 + 3.00) ÷ 4 = 12.10 ÷ 4 = 3.025


After calculating this, divide this result—the Average Table Diameter—by the Average Girdle Diameter and multiply by 100.

Then round it off to the nearest percentage.

For an Example:

If the Average Table Diameter = 3.025 mm, and the average

girdle diameter = 4.333 mm, then

Table percentage = (3.025 ÷ 4.333) × 100

= 0.6981 × 100 = 69.81, round it to 70%

And you've got it. It's that simple


Here are my recommendations on Tools for measuring Table Gauge in Diamond and Gemstones

I love this. It's one of those tools that you might not need it daily but it's great to have it just in case.

Find yours on the GIA Store HERE

Price: $21.95

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