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AGS Certification: Everything to Know Before Buying a Diamond

AGS and GIA are grading organizations that have the greatest reputation in the diamond industry. Precisely, their reports have become a must-have document for a safe diamond purchase. But how did it happen? Mainly, because of the need to regulate the diamond trade and find a third party in judging diamond buyers and sellers.

Like GIA, AGS laboratory is a non-profit organization. This fact guaranteed objectivity in the reports and turned AGS into one of two top grading institutes on the diamond market. The particular scale AGS introduced is consistent, scientific, reliable, and widely accepted all over the world.

AGS is the first certification institute for diamonds ever established. It was founded in 1934 and aimed at providing scientific counterarguments to unfair diamond advertising in their reports. Such head start became the background for the current top quality of AGS diamond grading, especially in measuring cut.

AGS Diamond Grading: The Basics

These days, AGS certification became the global standard. To apply, you can refer to one of the AGS offices all over the world – in Belgium, Hong Kong, India, Israel, and China.

In their local offices, AGS will offer you a bunch of reports. Here are the most typical examples:

  • AGS Diamond Report, or a comprehensive certificate mentioning color, a plotted diagram for clarity, carat weight, and detailed description of cut (based on the details about proportions, polish, and symmetry)

  • AGS Gold Diamond Quality Report, or simplified representation of grades for color, cut, clarity, and carat weight. For your convenience, the certificate contains both AGS and GIA grading classifications.

  • AGS Platinum Diamond Quality Document, or the combination of Diamond Quality Analysis with a unique Light Performance map,

  • AGS Diamond Quality Analysis, or a brochure of the main scales for small diamonds, and

  • AGS Diamond Grading Consultation, or quick depiction of the key dimensions for diamonds less than 5 carats.

In each type of evaluation, at least two gemologists guarantee the highest standards of the process.

AGS Diamond Report: How to read

AGS diamond institute is the top organization in issuing reports for round diamonds. For every diamond shape, it builds the evaluation based on measuring all the key parameters.

Here’s the typical structure of the AGS Diamond Report:

  • Report number (the unique number of the AGS paper) and the date of its issue,

  • Shape (the description of the diamond shape),

  • Measurements (diamond length, width, and depth),

  • Proportions (Diamond table percentage, crown angle, culet, etc. to compose the one-word rating: Ideal, Excellent, Good, Fair, Poor),

  • Evaluation of cut grade (0 to 10),

  • Color grade scale (0 to 10),

  • Clarity grade scale (0 to 10),

  • Carat weight,

  • Comments (all the essential information that doesn’t fit the above-mentioned strict structure of the report),

  • Diamond profile (the collection of all the main measurements in one figure – including table percentage, crown, girdle, culet, and pavilion parameters and percentages, and also the total depth percentage),

  • Diamond plot (the unique representation of crown and pavilion only AGS diamond report shows),

  • Diamond flap (a visual diagram of 4C scales with Key to Symbols).

In addition to providing measurements that have many common features with other institutes, AGS diamond certificate features some highly specific scales for grading diamonds. Let’s investigate AGS grades in detail and compare the representation in their reports with GIA certification scales.

Diamond table percentage grade, Diamond width grade, and Depth percentage grade

First, to get the table percentage, AGS diamond grading experts divide the overall width of a diamond by its table width. This parameter is important because it tells a lot about the accuracy of proportions in a diamond.

Then, width helps to identify the exact percentages for the diamond table and depth. AGS diamond certification specialists calculate the length from one girdle side of a diamond to another, catching the widest diameter possible.

Finally, the depth percentage grade relies on the height from a culet to a table. For the exact percentage, diamond experts divide the total depth of a diamond by its overall width (both indicators are measured in millimeters).

All these parameters tell a lot about the symmetry and proportions of a diamond. But the most important dimension they help to measure is a diamond cut.

Cut in AGS diamond grading

AGS diamond grading has many similarities with GIA evaluation but still lots of differences. And cut grading category is a feather in the cap of this institute. In particular, AGS adopts a unique approach that is based on a simple scale from 0 to 10.

Here’s the detailed overview of the way AGS scale grades diamond cut in its certificates.


AGS Ideal Cut


AGS Excellent Cut


AGS Very Good Cut

3 4

AGS Good Cut

5 6 7

AGS Fair Cut

8 9 10

AGS Poor Cut

But what determines the quality of cut – and the grade prescribed? This parameter depends not only on the right numbers in measuring depth, width, and table but also on a cumulative effect of the harmony between these dimensions. Moreover, shape and carat weight can significantly change the exact proportion needed to guarantee maximum sparkle and brilliance. This factor will also affect cut quality.

Thus, each diamond should be evaluated individually to determine its accurate cut in the report. By sticking to this rule, AGS became known for its outstanding excellence in measuring cut dimension – especially when it comes to round diamonds.

Even comparing to GIA, AGS diamond evaluation is more professional in checking diamond cut. That’s because AGS is stricter in following the classic Tolkowsky model. Besides, this grading institute uses 3D technology to check the cut quality. In particular, AGS adopts hardware and software to create a model of a diamond and then evaluates it for light performance. The procedure features measuring brightness, sparkle, leakage, and contrast. Finally, the diamond professionals in AGS draw their conclusions on the cut quality after considering grades for table, culet, width, and depth. If everything is fine, the diamond gets the “triple zero” status.

Because of rigorous attention to the details, cut quality grading in AGS became the best of the best.

Color in AGS diamond grading

Diamond color determines the appearance of your precious stone. There are two main color categories: colorful (or fancy) and colorless. In your AGS report, you’re likely to see the grade for a colorless diamond – they are more common and easier to evaluate. Fancy-colored diamonds are scarce and rather placed on auctions.

Even though AGS and GIA have a similar methodology for grading diamond color, the exact titles they use are different. The color scale for AGS vs. GIA looks like this:

AGS diamond report

The meaning

GIA diamond report

0.0 0.5 1.0



1.5 2.0 2.5 3.0

Near Colorless


3.5 4.0 4.5



5.0 5.5 6.0 6.5 7.0

Very Light color


7.5 8.0 8.5 9.0 9.5 10.0

Light color


To evaluate the diamond color, both GIA and AGS certification use master color sets. An angle of 45 degrees is used to measure its. This grading method allows a one-grade deviation between GIA and AGS certificates.

Clarity and carat weight

Clarity is the diamond parameter that determines the presence of imperfections, along with their placement and size. The measurement scale for clarity commonly includes several grades that change with the increase and severity of blemishes and visible flaws.

Like it works with the diamond color, AGS diamond evaluation specialists follow the way GIA laboratories examine clarity. But AGS does this in its own naming manner. Here’s how to read diamond clarity from AGS certificate if you’re used to GIA diamond grading scale:

AGS diamond grading

GIA diamond grading


Flawless, IF

1, 2

Very Very Slightly Included (VVS1, VVS2)

3, 4

Very Slightly Included (VS1, VS2)

5, 6, 7

Slightly Included (SI1, SI2)

7, 8, 9, 10

Included (I1, I2, I3)

If you want to get the best value-for-money, search for 1 or 2 near the diamond clarity graph. 0 clarity is surely better, but you can take the lesser grade that looks perfect in an appropriate setting.

Finally, any diamond grading is accurate without measuring carats. The more carats a diamond has, the heavier it is – because each carat equals 0.2 grams. At the same time, the scale for measuring carats doesn’t predict the changes in diamond size. Here, the diamond shape becomes more important.

The optimized amount of carats is up to individual taste, intentions, and budget limits: 2-carat diamonds are more affordable, while 7-carat ones perfectly fit special occasions. But, of course, the ideal diamond cut is a must for all the cases.

Other diamond elements AGS works with

Additionally, AGS diamond evaluation includes polish, symmetry, and fluorescence in its reports. All these factors contribute to the creation of a perfect diamond appearance. Also, fluorescence is the reaction of a diamond to ultraviolet lighting, and it highly depends on the angle from which you look at it.

How to get a consultation on reading AGS diamond report?

If you got lost in your AGS report, can’t understand its scales, or feel incapable of identifying is everything wrong with the width of your diamond, you can always get in touch with Diamond Registry specialists! We have more than 60 years of experience in the diamond market and are experts in reading reports from any certification institute. Contact us by filling the request form below!

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