Best Diamond Certification Labs Ranked for 2025

Below are our ratings for the best diamond certifications and summarized insights about each lab's shortcomings.

The best diamond certification lab for reliable grading is GIA, which is widely regarded as trustworthy and consistent. HRD and GCAL are also considered reliable labs. The International Gemological Institute (IGI) has been improving its diamond grading process. However, the European Gemological Laboratory (EGL) has lost credibility and market share due to inconsistencies. Gemological Science International (GSI) is generally satisfactory, though occasional grade inconsistencies may arise. The Professional Gem Science Laboratory (PGS) is dependable but less well-known.

AGSL - AGS Certification

The American Gem Society (AGS) is a membership organization of jewelers, suppliers, appraisers, and traders. The company has been operating since 1934; however, its laboratories—the American Gem Society Laboratories (AGSL)—were founded in 1996 and merged with GIA in 2022. The organization also has an advanced instruments division, founded in 2004.

AGSL is primarily responsible for grading diamonds based on its own grading standards. It was a formidable rival to GIA and had a strong reputation in the diamond industry.

Con: Instances have been observed where AGS graded diamonds in the SI2 category as if they were more akin to I1 diamonds. Consequently, caution is advised when dealing with AGS's inconsistencies in grading clarity within the SI2 range.

Please note that AGS merged with GIA in late 2022. These insights are relevant to existing AGS grading reports, which can be verified here. 

GIA Certification

The Gemological Institute of America (GIA) is a non-profit organization researching and educating consumers about jewelry and gemstones. It studies and grades all types of gemstones. GIA's diamond grading reports are the industry's top-rated diamond "certifications" and verification documents.

Alongside its lab services, GIA trains gemologists and provides research support to the diamond industry.

GIA offers two types of diamond grading reports: full reports and small diamond dossiers. The dossiers are less expensive than the full reports and do not include a diamond's full plot showing the inclusions' exact location.

Because the locations of inclusions are not determined in dossier reports, GIA will require a mandatory laser inscription of the diamond. In full reports, the laser inscription is an added service for $30.

Con: As GIA has grown, the quality of its graded services seems to have suffered. Recently, we have seen GIA regard its own G-color-graded diamond as a lower H color.

Discussions also revolve around GIA's methodology for determining excellent cuts in diamonds. A point of contention pertains to the broad criteria for assigning excellent cut grades to diamonds – the highest tier on GIA's scale. In comparison, it has been suggested that AGS's utilization of a proportion-based system for assigning ideal cut grades in their reports may yield a superior grading approach.

For those considering well-cut GIA graded diamonds, evaluate the GIA's cut grade against our recommended super ideal cut proportions.

GIA diamond reports can be verified here.

Gem Certification and Assurance Lab

The Gem Certification & Assurance Lab (GCAL), founded in 2001 by Donald A. Palmieri, is a leading third-party diamond grading laboratory known for its commitment to transparency and accuracy. GCAL provides reliable certification through independent, detailed analysis of diamonds, ensuring their value aligns with their cost. The lab's rigorous standards, including advanced technologies like Gemprint and ISO 17025 accreditation, help protect consumers from inflated grading and unethical practices. GCAL's emphasis on fairness is further demonstrated by its unique Guaranteed Diamond Grading Certificates, offering a money-back guarantee for accuracy. With a focus on quality, consistency, and integrity, GCAL remains a trusted name in the diamond industry.

Con: Besides having a small market share (which is growing), GCAL is exceptional in all departments and the only lab that actually certifies diamonds.

CGAl's diamond certification can be verified here.

HRD Certification

HRD Antwerp, closely linked to the Antwerp World Diamond Center, plays a significant role in the diamond trading and supply sector. Established in 1973, HRD represents the Belgian diamond industry. The HRD Lab adheres to standards similar to those of the GIA and follows grading regulations set by the International Diamond Council, underlining its reliability.

Weakness: It is worth noting the possibility of one grade inconsistency in HRD's grading when it comes to diamond color and clarity. 

HRD reports can be verified here.

IGI Certification

Founded in 1975 and headquartered in Antwerp, the International Gemological Institute (IGI) has a global presence, with multiple branches and a gemology school. However, IGI's widespread reach results in slightly varying grading criteria among its labs in different countries.

While still a major player, IGI's accuracy is generally considered somewhat lower than that of GIA or AGS. Therefore, expect one-grade inconsistency when buying IGI-graded diamonds. However, no two diamonds are identical, so applying a generalized approach to buying diamonds is not a good idea. Each case is different and should be treated differently.

Con: expect a degree of grading inconsistency across all 4Cs regarding IGI's grading.

Buyers can verify an IGI-issued report here.

GSI Certification

Gemological Science International (GSI) primarily grades diamonds for large chain stores, focusing on high-volume grading. With a global expansion, GSI's appeal to large stores lies in its ability to offer expedited diamond grading services compared to GIA or AGS.

While its accuracy in diamond grading is comparable to IGI's, GSI often assigns slightly lower grades than GIA or AGS. Nonetheless, due to the distinct characteristics of each natural diamond, individual evaluation remains crucial.

Opting for GIA or AGS certifications is advisable for those without comprehensive knowledge or the time for exhaustive research.

Con: Prudence is recommended when assessing GSI-graded diamonds, as some grade inconsistencies may occur. Seeking the expertise of a third-party expert can be beneficial. 

GSI reports can be verified here.

EGL Certification

The European Gemological Laboratory (EGL) once held a significant stake in the diamond grading realm. However, it has lost much of its credibility. The organization is reorganizing, and, for now, it is best to avoid their grading reports. Due to its diminished reputation, RapNet has excluded EGL-graded diamonds from its platforms.

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

EGL reports can be verified here.

Understanding the process of diamond grading itself is essential for making well-informed decisions regarding various diamond grading reports and certifications.

The major grading laboratories employ remarkably similar procedures for assessing and grading diamonds. The process typically involves multiple graduate gemologists independently evaluating a diamond's cut, color, clarity, and carat weight. The final grades are determined after all evaluations have been considered. This approach helps minimize the potential for human error in establishing a diamond's final grade, although it does not eliminate it.

Inconsistencies can arise when a diamond is reevaluated by a different lab, particularly when a stricter or more consistent lab reassesses a diamond graded by a less rigorous lab. Such inconsistencies are more pronounced among labs with varying grading standards.

Consistency in Results

One reason for AGS and GIA's dominance in the industry is their consistent and accurate grading. If a dealer sent a diamond to AGS or GIA for evaluation, they would likely receive very similar grading results with minimal discrepancies. Some level of slight variation is considered acceptable within the industry.

Organizational Structure Matters

AGS is a membership organization, while GIA is a non-profit entity. Both AGS and GIA are regarded as more objective than other labs when it comes to grading diamonds. Their organizational structures focus on maintaining consistent and accurate grading standards, influencing their objectivity.

On the other hand, some commercial labs are profit-driven and more customer-oriented toward diamond merchants, which can lead to discrepancies in grading results. Commercial labs may sometimes assign slightly higher grades on average than AGS or GIA to satisfy their clients.

Buyer's Perspective

Diamond certification is pivotal for buyers. While several grading labs offer diamonds, those graded by AGS or GIA are generally considered more reliable and consistent.

Be cautious of diamonds with grades similar to GIA's from other labs at significantly lower prices, as the reduced price may indicate lower quality.

Ultimately, when buying a diamond, especially for an engagement ring or other significant occasions, opting for a diamond graded by AGS or GIA is recommended due to its established reputation for accuracy and consistency.

One of the most significant advancements in the diamond industry during the 1950s was the introduction of GIA's cut grading system. This system played a pivotal role in standardizing diamond evaluation, aiming for consistent judgment across the industry. While the 4Cs of diamond grading were established concepts, and various other grading systems were in use, the necessity arose for a universal grading system. As a result, GIA's 4Cs grading system is the most widely adopted and accepted standard for diamond grading.

GIA's system meticulously evaluates a diamond's cut, assigning it one of five cut grades as outlined below:

Excellent Grade: Diamonds achieving this grade exhibit an even distribution of light and dark areas when observed, accompanied by pronounced brilliance and scintillation.

Very Good Grade: Diamonds within this category also display notable brilliance and scintillation but may have slightly more darkness in the center or around the edges. Additionally, the diamond's pattern holds significance. Sometimes, despite excelling in other aspects, a diamond might have an imperfect pattern, leading to a downgrade from "excellent" to "very good."

Good Grade: Diamonds in this range tend to be darker than those in higher grades or might lack sufficient brilliance and scintillation. The diamond's pattern quality is also of lesser caliber. Another factor influencing this grade could be the diamond's weight ratio. Some stones have an unusually high weight ratio, exceeding an average gem of the same diameter. In such instances, the diamond might be downgraded by one step.

Fair Grade: Diamonds assigned this grade often lack substantial brilliance or scintillation. Dark patches might be prevalent in areas like the table region or girdle. Poor cutting, noticeable imperfections in symmetry and proportion, and a lack of quality in the diamond's overall appearance can also result in this grade.

Poor Grade: Diamonds in this classification exhibit notable deficiencies. Due to flawed cutting, they generally possess subpar proportions and symmetry, resulting in limited brilliance and scintillation. This grade might encompass diamonds with "nail heads," characterized by a central black patch, or "fish eyes," where the center lacks brilliance. Once again, the diamond's weight ratio is a pivotal consideration.

Beyond brilliance, scintillation, symmetry, and weight ratio, GIA's diamond cut grading process also considers durability, including thin girdles and inclusions. Furthermore, polish quality, encompassing nicks, scratches, chips, and other surface imperfections, plays a role in the assessment.

AGS's proportion-based cut grade system has emerged as a formidable contender to challenge the dominance of GIA's grading system within the industry. Interestingly, AGS and GIA were initially funded by the same individual, Robert Shipley. However, differing opinions on the parameters and methodology for grading diamond cuts led to their divergence, with AGS establishing its lab and grading system.

In contrast to the comprehensive GIA system, which provides an overall designation based on multiple diamond features, AGS's proportion-based cut grade system assesses a diamond's color and clarity and cuts it individually. It assigns each aspect of the diamond one of 11 levels, ranging from 0 to 10—where zero represents the best and ten the worst. A diamond receiving three 0s attains a flawless cut featuring impeccable polish, proportions, symmetry, and optimal light performance.

Clarity Scale: As the name implies, the scale gauges a diamond's clarity and the presence of inclusions. A score of 0 signifies a flawless diamond devoid of visible inclusions, embodying impeccable clarity. Levels 1 and 2 fall under the "very slightly included" category, while 3 and 4 are labeled "very slightly included." The scale progresses to levels 5 and 6, indicating noticeable but slight inclusions. Levels 7 to 10 signify substantial inclusions, with ten being the most included.

Color Scale: Reflecting its name, the color scale assesses the diamond's color. A score of 0 to 1.0 signifies an utterly colorless diamond, conforming to the industry's ideal color standard. Levels 1.5 to 3.0 are designated as "near colorless," while 3.5 to 5.0 denote faint colorations slightly perceptible to the naked eye. Levels 5.0 to 7.0 reflect "very light" colorations, progressing to 7.5 to 10.0, characterized by light but more noticeable coloration. Beyond 7.5 to 10.0, diamonds acquire a fancy yellow hue, indicating lesser value.

Cut Scale: The cut scale evaluates the diamond's cut quality. A level 0 denotes a flawless cut with perfect symmetry, high brilliance, and scintillation. The diamond's polish is impeccable and free from nicks, scratches, or chips. Grades 2 and 3 signify "excellent" and "very good" cuts, respectively, with characteristics similar to an ideal cut diamond but without the same level of perfection. Levels 3 to 4 encompass "very good" diamonds, while 5, 6, and 7 represent "fair" cuts, indicating lower cut quality. Poorly cut diamonds with apparent flaws, faulty patterns and symmetry, low brilliance, and scintillation occupy the last range from 8 to 10.