How Are Diamonds Graded? – Defining Diamond’s Beauty [2021]

how are diamonds graded?

A diamond is a girl’s best friend. Just like our friends are different from one another, all diamonds are not the same. We know they come in different shapes and sizes. But, other factors make them different, if not better, than one another

In this article, you’ll understand

  • What Makes Each Diamond Different
  • How Diamonds are Graded
  • Why Some Diamonds are Valued More (or Less). 

By the end, you should be able to confidently inspect and analyze the diamond you’re getting the next time you shop.

How Are Diamonds Graded?

diamond grade

Diamonds are of the best-known and most coveted gemstones. Since ancient times, they have been used as decorative items or adornments. However, as pretty as they all are, each comes with different characteristics that define how valuable they are. These characteristics are what they are graded for.

Every diamond comes with a grading report that serves as an official grading of the gemstone’s quality.

If you are a gemologist or a lapidarist, you may already be aware of what is in the grading report and who grades them. But, if you are merely looking at making sure you are getting the best diamond, you’ve come to the right place. This article will give you a comprehensive explanation of everything you need to know about the diamond grading system.

Who Grades Diamonds?

Objective diamond grading organizations provide grading reports, analysis, or certifications for diamonds. These organizations have laboratories that use specialized equipment for diamond grading and analysis. Since they have their specific practice of scoring gemstones, results may differ for a diamond if analyzed by different labs.

For instance, Organization A may be looser in grading color, while Organization B may be strict with grading clarity. This is the reason diamond companies are sending their stones to different labs to maximize their results. Understanding which labs are reliable and consistent will keep you from buying diamonds worth less than what the grading declares to be true.

Two of the industry’s best diamond certification organizations are the GIA (Gemological Institute of America) and AGS (American Gem Society). Both are the most consistent in lab grading certifications. This consistency gives you confidence that you can trust their grading reports in all diamond aspects – which we will discuss as we go along.

Gemological Institute of America (GIA)

The GIA is a non-profit institute committed to research and education in the field of gemology. It is one of the world’s well-respected and renowned diamond grading authorities. From their institute are the most consistent and reliable certifications for diamonds.

Although the GIA has no financial stake in diamond sales, their team evaluates diamonds’ various qualities, characteristics, and elements. Such includes:

  • Evaluation date
  • Measurements (in mm)
  • Cutting style and diamond shape
  • Carat weight
  • Table percentage
  • Depth percentage
  • Culet size
  • Symmetry
  • Proportion diagram
  • Polish grade
  • Girdle thickness
  • Cut grade
  • Color grade
  • Clarity grade (IF, VVS1, VVS2, VS1, VS2, SI1, SI2)
  • Diamond plot with all blemishes and inclusions
  • Fluorescence grade
  • Laser inscription
  • Security features
  • General comments

The GIA has a distinction for rating rated Color and Clarity, more rigorously. After all, these two characteristics are the most subjective scales. Their reputation, backed with proven consistency and history, makes most jewelers and gemologists recommend only buying diamonds with their certificate.

Diamond sellers who offer GIA certificates with their gemstones are Blue Nile, James Allen, and Brian Gavin Diamonds.

American Gem Society (AGS)

Founded in 1934 by Robert M. Shipley, the American Gem Society is a trade association of retail jewelers, independent appraisers, suppliers, and selected industry members. The society has diamond grading as part of its specialty. So much that they also train and certify jewelers, gemologists, and jewelry appraisers.

The AGS takes pride in being the first lab to offer diamond cut grades. They have this criterion long before the GIA introduced their cut grade scoring.

The “ideal cut” market had been monopolized by the AGS back in the day. A diamond can’t be called “ideal” unless an AGS certificate declares so. With the GIA in the picture, the AGS’ share in the market plunged significantly.

diamond grading entities

Other diamond certification entities in the industry today are:

  • International Gemological Institute (IGI)
  • European Gemological Laboratory (EGL)
  • Hoge Raad voor Diamant (HRD)
  • Gemological Science International (GSI)

Although they are recognized as players in diamond certification, most retailers and experts do not recommend buying diamonds with their certification. Some of them have gradings that are looser than the GIA and AGS standards. Also, their procedures and classifications do not maintain consistency.

Grading Scales

The idea of shopping for diamonds may rush you with excitement – because you are shopping for the most beautiful stone! However, the fact that you are shopping for the most coveted gem makes the experience seem daunting.

Thus, institutions like the GIA and AGS came up with grading scales. These unbiased authorities offer this information to aid you in getting only the highest quality diamond.

These grading scales set the level for the diamond’s 4 Cs – color, clarity, cut, and carat weight.


A diamond’s cut is graded by relating its proportions with a set of benchmarks. These standards are prime diamond proportions found to boost some of the gem’s essential characteristics, specifically brilliance and sparkle.


For instance, one of the key ratios used to scale cut grade for round diamonds is the depth of the stone and the diameter of its table. This grading is expressed in percentages of the diameter of the girdle or the diamond’s widest edge.

For the GIA, cut quality is essential. Thus, the 15 years of study they put up to understand the factors contributing to the diamond’s appearance. The institute evaluates cut grade by:

  • How well it appears when viewed faced-up and how it shows its brightness, fire, and scintillation.
  • How well the diamond was designed to guarantee endurance and optimal weight.
  • How well the craftmanship that the diamond went through into aligning and polishing the facets.

GIA Cut Scale

ExcellentVery GoodGoodFairPoor

The GIA’s visual assessment includes brightness, fire, and scintillation. They look for the brilliance that comes from a combination of white light reflections from the stone’s internal and external surface in terms of brightness. For fire, they grade it by how the light is distributed into different colors of the spectrum. At the same time, they assess scintillation by the sparkle patterning when the diamond is tilted.

Compared to the GIA, the AGS uses a numerical system in their reports. The rating is from 0 – 10, where 1 is Excellent, 2 is Very Good, through 10, which is Poor.

AGS Cut Scale

AGS IdealAGS ExcellentAGS Very GoodAGS GoodAGS FairAGS Poor

The AGS follows aspects of the diamond’s cut by the crown and pavilion angle, pavilion depth, girdle thickness, table diameter, polish, culet size, performance, and symmetry. Comparatively, their cut grading system uses a more scientific approach that provides better objectivity when analyzing a diamond’s cut grade.

Buying Tip:

Cut is the most crucial factor in diamond grading. Excellent color or quality won’t even matter as much if the diamond is poorly cut. If you want superior brilliance, go for diamonds with a cut grade of Very Good or Excellent for round and Good (or better) in other shapes.

Carat Weight

Diamonds are marketed by the carat (ct). Carat is its unit of weight, although a lot mistake it to the diamond’s size. The term “carat” derives from the Greek word “carob.” In the earlier days, the seeds of the carob pod were used as standards for weight measurements because the seeds’ size are almost always identical.

carat weight

Nowadays, a carat is equal to exactly 0.2 grams or about the weight of a paper clip. While some may think diamond carat do not matter because the eyes doesn’t see the weight, they do. The value of a diamond rises as the carat size increases.

Buying Tip:

Pick diamonds that fall just under the well-liked carat weights like ½ ct, ¾ ct, or 1 ct. These diamonds come in just shy of the popular weight and are sold at a slightly discounted price than full carat weight.


Diamonds come in different colors, with some even highly prized like pinks, blues, and even yellow. But, in the white diamond industry, a tinge of a yellow color may lower the diamond price. In this department, the less body color in a white diamond, the more true color it shows, and the grander its value become.

The GIA’s definitive diamond color scale begins with the letter D that corresponds to colorlessness. The scale continues to the letter Z. The farther it is in the diamond, the more yellowish, little brownish, or grayish it is.

The color grades from the GIA Color Scale are subdivided into different subcategories:

GIA Color Scale
ColorlessNear ColorlessFaintVery LightLight

The AGS, on the other hand, has their color scale on a 0 to 10 scale. They needed to give a more accurate and specific description of the diamond’s color by using a numeric scale. This method lets buyers have a better identification of the diamond’s color.

AGS Color Scale
00.511.522.533.544.555.566.577.588.599.510To Fancy Yellow
ColorlessNear ColorlessFaintVery LightLightFancy Yellow

What’s interesting about diamond color is that even when colorless ones are highly-priced, many diamond buyers still prefer one that has a slight yellow touch because it feels and looks warm.

Buying Tip:

The best value for your money is one that would appear to the naked eye as colorless. Most diamonds under G to J grade are. Color in larger diamonds is easier to detect, so go for G to H in diamonds over 1 ct, or I to J for stones under 1 ct. Rather than spending your money in a higher color grade, invest in a higher cut grade since brilliance is the diamond’s most important factor.


Since diamonds are formed deep within the earth and in extreme heat and pressure, they may contain birthmarks – tiny flaws inside the diamond or inclusions and imperfections on the surface or blemishes. Diamond clarity is the degree to which these imperfections are existing.

The inclusions or blemishes in diamonds affect the diamond’s brilliance because the flaws interfere with the path of light through the stone.

Diamonds are graded for clarity using the diamond clarity scale. For the GIA, its scale has six categories:

  • Flawless (FL) – no inclusions or blemishes under 10x magnification
  • Internally Flawless (IF) – no inclusions visible under 10x magnification
  • Very, Very Slightly Included (VVS1 and VVS2) – Slight inclusions that are difficult even for a skilled grader to see
  • Very Slightly Included (VS1 and VS2) – Inclusions are observed with effort under 10x magnification yet can be classified as minor
  • Slightly Included (S1 and S2) – Inclusions are visible under 10x magnification
  • Included (I1, I2, and I3) – Obvious inclusions under 10x magnification

GIA Clarity Scale





Internally FlawlessVery, Very Slightly IncludedVery Slightly IncludedSlightly Included


In uniform with the AGS’ diamond grading scales, their clarity scale is in a numerical format, too. It is from 0 to 10, with 0 as the GIA’s FL equivalent.

AGS Color Scale
FL / IFVery, Very Slightly IncludedVery Slightly IncludedSlightly IncludedIncluded

Buying Tip:

If you cannot put up with imperfections, even those too tiny to see, go with a VVS2 or better. About 10% of all diamonds sold fall into this classification.

History of Diamond Grading

Even before the GIA and AGS came into the picture to set the standards of the 4Cs in diamond grading, a lot of different methods have been used to record and analyze a diamond’s quality during the Kimberley diamond rush.

For instance, diamond graders applied multiple As (AAA, AA, A), numbers (1, 2, 3), or Roman numerals (I, II, III, IV) to define colorless diamond.

These grading methods worked perfectly with local traders. The problem came in when diamonds were started to be traded internationally. In most cases, diamond graders throughout the world used various types of grading systems. Thus, the difficulty in getting the accurate value of the diamond back then.

The GIA wanted to standardize diamond grading for international trading. Their grading scale is now the universal diamond grading system used to avoid unnecessary confusion.


As a diamond buyer, you have to understand that a diamond is an organic whole. They were formed from carbon some hundred feet below the ground, and the carbon (like the diamonds) that shaped them was also subjected to intense pressure and heat.  These subsequently caused crystallization.

The four qualities of a diamond that we described are the key components that impact its beauty, structure, and value. All of them interact with each other within the diamond, dictating how the diamod appears and how high its quality is.

Having said that, a diamond should be judged as a whole instead of by the element, such as cut or color. Every characteristic is essential, and they combine to form the beauty and brilliance that a diamond has to be.

Professionals use reliable scale grades to analyze these characteristics. With a better understanding of the diamond’s 4 Cs, you can better decide if the diamond is of the best quality.

FAQs (Frequently Asked Questions)

Q: How vital is a diamond certification?

A: Diamond grading or certification verifies and defines the stone you are purchasing. Without it, there is no exact way to know whether the diamond you are getting is indeed what the seller claims. This piece of paper indicates details like cut quality, color grade, carat weight, and clarity. As with most expensive things you buy, the legitimacy proof of what you are buying is always essential.

Q: Is there a difference between a certified and non-certified diamond?

A: They differ in terms of the previous having proof that they are what they claim to be and the latter, without. A certified diamond has been thoroughly evaluated and comes with a certificate. A non-certified diamond does not. You can better trust a certified diamond since it is verified and confirmed by professionals and reputable agencies. Non-certified diamonds can be doubtful because there is nothing that backs them up.

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