Diamond Certificate Comparing: Everything To Know

The most renowned and trusted gemmological grading laboratories are the Gemological Institute of America (GIA), the American Gemological Society (AGS), the Hoge Raad voor Diamant (HRD), the International Gemological Institute (IGI), and the 2 versions of European Gemological Laboratory (EGL International and EGL USA). From these 5 laboratories, the 3 that set the standard are the GIA, AGS & HRD.

The GIA is widely regarded as the most reputable and recognized grading laboratory in the world, with the strictest standards. Founded by the creator of the GIA, The American Gemological Society (AGS) is a newer certification and markets itself around the fact that it offers an Ideal cut grade which is one higher than the Excellent from GIA and is as strict as GIA in every respect. The Hoge Raad voor Diamant (HRD) or Diamond High Council is almost as renowned worldwide as GIA but not as popular and it is 95% as strict in its grading.

BEWARE - Even though these are the 5 leading international diamond certification organisations their grading criteria do vary and are not equally strict. Please be aware of the differences when choosing your diamond (see below).

All the certificates differ slightly in layout, terminology and grading systems, with some including diagrams and symmetry or proportion grading and others being simpler. However, the two main grading aspects to consider when comparing certificates are color and clarity, for their evaluations largely determine the price of a diamond and yet they are not consistently graded across the board. A color grade, for instance, may differ in up to two grades (sometimes more) from one certificate to another and yet this is not always reflected in the price, so beyond understanding simply how color or clarity grades work, it is essential to know how to interpret and compare them.

Besides the 5 popular types of certificates that reputable jewellers offer, there are a multitude of other types of certificates not always independent, such as "in house" certificates which are typically graded more generously even than EGL International certificates and which cannot be compared with independent internationally recognised certificates.

Diamond Certificate Comparison - For Color Grading

Overall, the GIA tends to be the strictest on color grades, and out of the other laboratories, HRD and AGS are the two that most closely adhere to the standards set out by the GIA. IGI and EGL USA tend to give one color grade higher than GIA, and EGL up to 2 color grades higher. So an F color stone on a GIA certificate would most likely be the same on HRD and AGS, an E on IGI or EGL USA, and a D on EGL. Please refer to the table below for a more detailed comparison* (note - table is based on our experience):

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Diamond Certificate Comparison GIA AGS HRD IGI EGL USA EGL INT. In-house Certificates
White D D D D+ D+ D+ D+
White E E E D D D+ D+
White F F F E E E+ D+
White G G G F F E D
White H H H G G F+ D/E
Extremely faint yellow tint I I I H H F E/F
Very faint yellowbrown tint J J J I I G F/G
Faint yellowbrown tint K K K J J H G/H
Yellowishbrownish tint L L L K K I H/I
Medium to strong yellowishbrownish tint M M M L L J I/J
Strong yellowishbrownish tint N N N M M K K/L
Very strong yellowishbrownish tint O-P O-P O-P N N L L/M

Certificate comparisons for color.

* Note - Although not published anywhere, these differences are generally accepted within the diamond trade as correct and are also based on our experience.

Diamond Certificate Comparison - For Clarity Grading

When it comes to comparing lab grading entities, it's more important to watch for consistency than strictness of grading. For example, the GIA will not grade a diamond the same way the IGI rates a diamond. The reliability of the color and clarity grades and in some instances the cut grades is only as good as the certifying lab's reputation. But if one lab consistently gives a single clarity grade higher than another lab, that lab is by no means less authentic:

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Diamond Certificate Comparison GIA AGS HRD IGI EGL USA EGL INT. In-house Certificates
100% Eye Clean FL/IF IF LC+ IF+ IF+ IF+ IF+
100% Eye Clean VVS1 VVS1 LC-/VVS1 IF-/VVS1 IF IF+ IF+
100% Eye Clean VVS2 VVS2 VVS2 VVS2 VVS1 IF+ IF+
100% Eye Clean VS1 VS1 VS1 VS1 VVS2 IF IF+
100% Eye Clean VS2 VS2 VS2 VS2 VS1 VVS1/VVS2 IF+
80% Chance SI1 SI1 SI1 SI1 VS2 VVS2/VS1 VVS1/VVS2
10% Chance SI2 SI2 SI2 SI2 SI1 VS1/VS2 VVS2/VS1
Not Eye Clean I1 I1 P1 SI3 SI2 VS2/SI1 VS1/VS2
Not Eye Clean I2 I2 P2 I1 SI3 SI1/SI2 VS2/SI1
Not Eye Clean I3 I3 I3 I2 I2 SI2/SI3 SI1/SI2
Not Eye Clean N/A N/A N/A I3 I3 I1 SI2/SI3

Certificate comparisons for clarity.

* Note - Although not published anywhere, these differences are generally accepted within the diamond trade as correct and are also based on our experience.

Other Differences Between Diamond Certificates

The main other differences between the certificates lie in the differences between GIA, HRD and AGS. GIA gives separate grading for symmetry and polish which the HRD groups together under the heading of "finish." HRD also includes one clarity grade termed "Loupe Clean" which is not offered by the GIA. The AGS provides more information on the cut grade and offers one grade higher than the traditional poor-to-excellent scale of GIA, called "ideal cut," as well as a number scale from 0-10 on which to grade diamond cut.