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The Ideal Cut Diamond

“It’s ideal!”

Ideal cut diamonds are solely determined by proportions and percentages that maximize the appeal of a diamond.

The ideal cut was created by a man named Marcel Tolkowsky.

Marcel created the ideal cutting style in 1919.
First we’ll look at the traditional ideal cut, and then we’ll look into the new GIA cut grade standards for ideals.

The Girdle

To understand the percentages of an traditional ideal cut, you also need to understand the width of the girdle. The girdle, which is the outer edge of the diamond, is the widest part of the diamond. No matter what the carat weight is, that girdle will always be equal to 100% of the width. Since nothing is wider than that, the rest of the diamond’s proportions are compared to it.

Diamond percentages (like 57%) always refer to the proportion of distance in relation to the girdle.

For example…

Look at the table of the diamond (shown below). The table is the top flat section of the diamond. The width of the table, as compared to the width of the girdle, is how you get the table percentage. An ideal cut table should measure between 53-57% of the width of that girdle.

Which brings us to the…

60/60 rule of thumb

Most jewelers tend to carry diamonds that have a little bit bigger table, like 60% width.

They do this because the diamond tends to look bigger and brighter. Personally, I also prefer a table around 60%. 60% makes a diamond appear slightly larger, but still give you plenty of brilliance and fire.

Ideal cut proportions and percents are shown below.

Ideal Cut Proportions!

The ideal total depth of an ideal diamond will fall between 57.5-63%

Just think 60%

This percentage total is the depth of the crown, girdle and pavilion height all added together.

Table and depth are the two most important figures to grasp. If you can get within a couple of percentages of these numbers (60%/60%), one way or the other, you’ll end up with a great looking diamond that’s full of life, fire and brilliance.

Granted, there are many other proportions to consider as well, but table and depth are the most important factors. If they are close to ideal, then the rest of the diamond should be close as well.

Ideal cut facets

Below is a chart that shows all the different facets of an ideal cut diamond.

Ideal Cut Diamond Facets!

Ideal cuts will be more expensive than poor cuts. Think about this if you see a diamond priced at half the price of other similar quality stones. Quite often that discount is attributed to the cut being off, or less than ideal.

The funny thing about ideal cuts is that ideal cuts are not really ideal. They are a range of percentages and guidelines. The depth percentage isn’t just one number, it’s a range of numbers between 57.5% and 63%. See, even an ideal cut has some degree of variance.

Best advice:

Don’t be too concerned with percents. If you get close to the standards, you’ll get a good amount of both white light and colored light in the stone. With this awesome balance your diamond will shine like crazy.

Diamond certificates will list the exact percentages right on the diamond report. Make sure you check them out to see where your table and depth lie…


Let’s hope so…


Now… Let’s look at diamond grading TODAY.

GIA (The Gemological Institute of America – the institute that devised the 4C’s and the standard diamond grading used today) updated the cut grades not too many years ago for “ideal” diamonds and simplified cut for everyone.

New GIA cut grades

GIA came up with cut grades that helps everyone understand cut way better than looking at percentages (like the 60%/60%). They created 5 cut grades that tells you how well a diamond is cut.

They are:

  • Excellent
  • Very Good
  • Good
  • Fair
  • Poor

With these 5 new grades…

Cut is easy to understand.

An excellent cut grade is the ultimate ideal cut diamond.

Excellent is the best of the best and there is no better.

Excellent grades will get you a diamond that will sparkle like a million stars in the sky.

So instead of looking for table and depth percentages, all you have to do is to look at a GIA diamond report, and look for “excellent” listed under “cut“.

Easy as that.

Cut is the most important factor when it comes to sparkle and beauty.

So there is no reason to buy ideal (really excellent).

Find some incredible ideal cut excellent diamonds here at James Allen.

Cheers! :)


  1. Very informative.. thank you!

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