Best Diamond Certification Labs in the World

Best Diamond Certification Labs in the World

Best Diamond Certification Labs in the World

Posted by Sharif Khan on 14th Jul 2021

Diamond "Certification" or Grading Labs

The price you pay for a diamond largely depends on how the diamond is graded in a grading report and/or "certificate.”

Grading reports by the Gemological Institute of America (GIA), HRD Labs, American Gem Society (AGS), and Gem Certification and Assurance Lab (GCAL) command the highest premium in the diamond industry. However, among the other labs, there are significant discrepancies in how they grade diamonds and assess the 4Cs.

Check James Allen's 3D 360 degree image technology for assessing the cut of GIA graded diamonds before buying them.

Please carefully review our ranking below for best diamond certification labs in the world. We have also provided additional insights on each lab in the subsequent sections.  

Diamond Certification Ranking

James Allen

Check our additional insights below about AGS vs GIA grading systems and where one may have an edge over the other. Overall, GIA is still considered as the standard-bearer in the diamond industry when it comes to grading diamonds. Furthermore, check this article on IGI vs GIA for your review as well.

Here is in depth video on diamond certification by Sharif:

Key Takeaways on Diamond Certification:

In short, diamond certification or grading is extremely important. Do not buy a diamond that is not graded by a reputable lab. Local jewelers will try to justify why a grading report is not necessary and try to convince you into buying an ungraded diamond. By doing so, even if they succeed in selling you a diamond that is one grade lower, their profit will be substantially higher.

Reputable diamond dealers will often send their stones to GIA for grading in order to be consistent and because they appreciate transparency. GIA is extremely strict and professional in grading diamonds. 

The only factor where you need more preparedness is how to assess the Cut grade in GIA's grading reports. 

They offer a cut grade in round diamonds only. Even in round diamonds, our guidelines on ideal proportions for each shape are critical and will help you distinguish between a super ideal cut vs an average excellent cut. 

Always verify a GIA grading report here.

AGS is also a top grading lab, but it can be at times slightly inconsistent in grading clarity and color accurately. At the same time, they are the best in grading the cut grade of a diamond because they use a proportion-based system.

IGI is a decent lab but not as good as GIA or AGS. If you are buying a lower color grade diamond (I-J-K), IGI is a perfectly fine lab. However, if you buying a premium grade diamond, always stick with GIA or AGS.

GCAL is a great lab but has a small market share. They are on par with GIA. Therefore, if you see a GCAL graded diamond, do not hesitate to purchase it. Often a GCAL diamond will also come with a GIA report.

Getting conflicting opinions on diamond labs is common because dealers will often tailor their opinions in favor of a lab that might have graded their diamonds. In order to make a better decision, follow our in-depth diamond guide for each shape.

An Illustration of GIA Excellent Cut vs AGS Ideal Cut Diamond: (Click on each image to watch a 3D Video of the Diamond).

James Allen Brian Gavin Diamonds

If you are shopping for high-quality AGS graded ideal cut diamonds, check out Whiteflash. They have the largest selection of in-house AGS graded diamonds.

A Review of Each Diamond Certification Lab:

In short, we highly recommend GIA as the top lab and consider AGS, HRD, and GCAL as reliable labs as well. The International Gemological Institute (IGI) is also improving its process for grading diamonds. Unfortunately, The European Gemological Laboratory (EGL) has lost much of its credibility and market share. The Gemological Science International (GSI) is an okay lab and at times might have one or two grade inconsistencies. The Professional Gem Science Laboratory (PGS) is also a dependable lab but does not enjoy much popularity. Moreover, GCAL is a very reputable lab.

GIA Certification:

The Gemological Institute of America is a non-profit organization dedicated to researching, and educating consumers, about jewelry and gems. They study and grade all types of gemstones. In addition to the lab services, GIA also trains gemologists and offers in-depth education and research support for the diamond industry. Presently, GIA’s diamond grading reports are top-rated diamond “certification” and verification documents in the industry.

GIA offers two types of diamond grading reports -- full reports and diamond dossiers for small diamonds. The dossiers are less expensive as opposed to the full reports and do not include the full plot of a diamond that show the exact location of inclusions. Because the locations of inclusions are not determined in dossier reports, GIA will require a mandatory laser inscription of the diamond. This, however, is not the case with full reports. Diamond dealers have the option to buy the laser inscription as an added service in full reports for an additional $30.


There are discussions on how GIA determines excellent cuts in diamonds. One issue with their grading is believed to be their broad criteria when assigning excellent cut grades to diamonds; excellent cut grades being the highest in GIA’s scale. It has been suggested that because AGS uses a proportion-based system for assigning ideal cut grades in their reports, its grading is superior to that of GIA. Please look up diamond proportions and use our chart to buy a well-cut GIA graded diamond. 

AGSL - AGS Certification

The American Gem Society is a membership organization of jewelers, suppliers, appraisers, and traders. The company has been in operation since 1934; however, its laboratories—the American Gem Society Laboratories (AGSL)—were founded in 1996. They also have an advanced instruments division founded in 2004. AGSL is the division that grades diamonds and has developed its own standards for doing so. It is a close competitor to the GIA and has a strong reputation in the diamond industry.


When it comes to grading a diamond's clarity, AGSL is not as strict as GIA. We have noticed diamonds in the SI2 range graded by AGS that GIA would not assign SI2 grades to. So, when it comes to clarity grading in the SI1/SI2 range, be wary of AGSL's inconsistencies.

HRD Certification

HRD Antwerp is mainly owned by the Antwerp World Diamond Center founded in 1973 which represents the Belgian diamond industry. As you might know, Antwerp is one of the main centers for diamond trading and supply. The HRD Lab’s standards are similar to the ones used by the GIA. They also follow grading rules set by the International Diamond Council and are extremely reliable.


Please note that we normally assume that there would be a grade inconsistency in HRD's grading when it comes to the grading of diamond color and clarity. Please consider this as you buy HRD graded diamonds. 

IGI Certification

The International Gemological Institute was established in 1975 and is headquartered in Antwerp—one of the key centers for the diamond industry. IGI has several branches worldwide, is one of the largest labs in the world, and also has a gemology school. Owing to the fact that IGI is extremely large spanning across the world, their labs in different countries seem to use slightly different criteria while grading diamonds. We would rate IGI as slightly less strict than GIA or AGS. You can expect one grade inconsistency while buying IGI graded diamonds. However, no two diamonds are identical, and so applying a generalized approach when it comes to buying diamonds is not a good idea—because each case is different, it ought to be treated differently.


You can expect one grading inconsistency in the overall grading when it comes to IGI's grading in all 4Cs.

GSI Certification

Gemological Science International mainly grades diamonds for some large chain stores in mass numbers. Recently, they have expanded their operations to a number of countries worldwide. GSI is a favorite choice of large stores because they grade diamonds much faster than GIA or AGS. It is close to IGI in grading diamonds and usually grades diamonds one grade lower than GIA or AGS. Again, as it has already been stated, because each diamond will have its own characteristics, it is important that diamonds are considered individually. 

If you are not well-informed or if you do not have the time to do the necessary research, go for either GIA or AGS.


It is wise to be cautious when evaluating GSI's diamonds. Expect a grade inconsistency and make sure you run the stone by an expert and get a third party opinion. The sad part is that most appraisers are unreliable, and so you will most likely be making a trade-off when buying GSI graded diamonds.

EGL Certification

The European Gemological Laboratory used to have significant shares in the diamond grading business; however, it has lost much of that credibility. They are reorganizing the organization, and, at least for the time being, you should not rely solely on their reports. As a result of their bad reputation, even RapNet does not allow EGL graded diamonds to be listed on its platform.


It is a safe bet to avoid EGL graded diamonds unless they are from the era of 1950s to the early 2000s. Even among these, you should expect up to two grade inconsistencies in the overall grading.

How are Diamonds Certified?

In order to make an informed decision on the various diamond grading reports/certifications, it is critical to understand how diamonds are graded in the first place. 

The major grading labs have remarkably similar processes for analyzing and grading diamonds. The process usually involves several graduate gemologists independently assessing the cut, color, clarity, and carat weight of diamonds with the final grades being extracted after all the assessments have been evaluated. The process helps to reduce the potential for human error in the determination of a diamond’s final grade, but it does not entirely eliminate it. 

Some labs are known to have inconsistencies when grading diamonds for the second time. This inconsistency is more noticeable when a diamond is reevaluated by a more consistent/stricter lab.

Diamonds are not certified; no lab would say that they are "certifying" diamonds. Legally speaking, it can cause them trouble, and so all they confirm is that they have graded a particular diamond based on their best opinion/assessment as represented in the grading report.

Consistency of result:

Part of the reason behind GIA's and AGS's dominance is their consistency, in that they are able to consistently grade diamonds accurately. If you were to send a diamond to GIA or AGS for evaluation, you would probably receive identical grading results without major discrepancies. 

A small difference is an acceptable norm within the industry though.

The organizational structure of each lab matters:

GIA is a non-profit organization. As such, GIA is known to be more objective than other labs when grading diamonds. 

Other labs are influenced by profit motives and are more customer-oriented; the customer being diamond merchants. As a result, the disparity in grading results is an open secret in the industry. Sometimes, commercial labs would give diamonds one point higher grading on average than that given by GIA to make their clients happy. 

If you find a diamond with similar grades from a different lab with a lower price than one being graded by GIA, do not be misled by its bargain price as the stone might be of lower quality and hence the price difference. 

Principally, from a buyer’s perspective, diamond certification is critical when buying a diamond. While there are many labs out there, your best bet is to buy a diamond that is graded by GIA or AGS. 

More Details on GIA and AGS Grading Systems

The GIA Diamond Cut Grading System

The most important innovation in the diamond industry in the 1950s is, undoubtedly, GIA’s cut grading system introduced to serve as the standard for which all gemstones and diamonds are specifically judged. Although the 4Cs of diamond grading were already well known and there were a number of other grading systems in use, it became necessary to have a uniform grading system to promote consistency across the industry. Today, GIA's 4Cs grading system is the most widely used and accepted grading standard for grading diamonds. 

The key features of a diamond that the system considers when assigning a grade are: color; clarity and make, comprising of the cut, polish and finish. There are five grades a diamond may be assigned after being evaluated by GIA:

Excellent Grade – Diamonds with this grade will have an even pattern of light and dark areas when one looks at the stone as well as high brilliance and scintillation.

Very good Grade – Diamonds in this category will also have high brilliance and scintillation but with greater darkness in the center or around the edges. The pattern of the diamond is also a major consideration. Sometimes, a diamond may be top-notch in all other aspects apart from its pattern that might be imperfect, resulting in a drop from the “excellent” grade to a “very good grade”.

Good Grade – Diamonds falling in this range will generally be darker than those in the higher grades or will have insufficient scintillation and brilliance. The pattern, moreover, will also be of lesser quality. A diamond could also get this grade as a result of its weight ratio; a diamond has an unduly heavy weight ratio when it is heavier than an average gem of the same diameter. In such an instance, it will be downgraded one step.

Fair Grade – A diamond with this grade will generally be one that seriously lacks brilliance or scintillation. It could have dark patches in major areas of the diamond, such as the table area and/or the girdle. Faulty cutting and noticeable imperfections in the symmetry and proportion of the diamond could also be reasons why it has been put in this grade.

Poor Grade – The diamonds that fall into this category are those with markedly faulty features. They will generally have very poor proportions and symmetry as a result of poor cutting with very little brilliance or scintillation. It is in this category that you will find “nail heads” wherein the stone has a black patch right in the center. It will also have “fish eyes”, meaning that the brilliance is totally washed out in the middle. Here again, the weight ratio of the stone is an important consideration.

Apart from features like brilliance, scintillation, weight ratio, and symmetry that have been discussed above, other factors considered by GIA diamond cut grading process include durability, including thin girdles and inclusions. These inclusions act to weaken the gem and polish, which covers the overall quality of the stone’s surface polish, noting any nicks, scratches, chips, etc.

AGS Proportion-Based Cut Grade System

The AGS proportion-based cut grade system is a major challenger to GIA grading system for dominance as the industry’s standard grading system. Both AGS and GIA were funded by the same person, the famous Robert Shipley. But, on account of disagreements over the parameters and methodology by which diamond cuts should be graded, both organizations drifted apart, leading AGS to establish its own lab and grading system.

As opposed to GIA system which gives an overall designation based on taking all the diamond’s features into consideration, AGS’s proportion-based cut grading system considers the color, clarity, and cut of the diamond and assigns each feature of the diamond one of 11 levels ranging from 0 to 10—0 being the best while 10 the worst. A diamond that receives three 0s is one that has been cut perfectly, carrying a flawless polish and perfect proportions and symmetry. Such a diamond must also have the best possible light performance.

Clarity Scale – The clarity scale, as the name implies, measures the clarity of a diamond and the extent to which it contains inclusions. A 0 level on this scale indicates that the diamonds are flawless and include no noticeable inclusions, making the clarity unblemished. Levels 1 and 2 are described as being “very very slightly included” while levels 3 and 4 are “very slightly included”. Diamonds that are given levels 5 and 6 on this scale will have noticeable, albeit still slight, inclusions. Diamonds given levels 7, 8, 9, and 10 will have substantial inclusions simply described in the grading system as “included”.

Color Scale – The scale measures exactly what its name says; the color of the stone. A diamond that is assigned a level of 0 to 1.0 is one that is completely colorless and meets the industry ideal regarding diamond color. Those with 1.5 to 3.0 are described by the grading system as being “near colorless”, while those from 3.5 to 5.0 have faint colorations that are just slightly visible to the naked eye. Diamonds graded 5.0 to 7.0 have “very light” coloration, whereas the coloration present in those with levels 7.5 to 10.0 is still light, albeit more noticeable. Any diamond with coloring beyond 7.5 to 10.0 will be one with the fancy yellow color and is considered less valuable.

Cut Scale – This measures the quality of the diamond’s cut. A diamond with a 0 level will be one that has a flawless cut and perfect symmetry. Such a diamond may even have a pattern of light and dark areas when viewed, possessing high brilliance and scintillation. The polish of the diamond is perfect and it is totally lacking in any nicks, scratches or chips. Diamonds with grades 2 and 3 are “excellent” and “very good”, respectively. Although they have similar characteristics as an ideal cut diamond, they do not have the same grade of perfection and flawlessness. Levels 3 to 4 comprise of diamonds that are described by the grading system as “very good” while those with 5, 6 and 7 are “fair”, which reflects a lower quality of cut. Poorly cut diamonds with obvious flaws, faulty patterns, and symmetry, low brilliance and scintillation occupy the last range from 8 to 10.


In this article, we offer comprehensive insights on diamond certification and grading systems available worldwide. Herein, we have also tried to elaborate on the reasons why certain jewelers/dealers will try to convince you that grading a diamond is not necessary and that you will be better off without it. We hope this article will enable you to make a better, more informed decision.