How Diamonds Are Rated?

When purchasing something as magnificent and as expensive as a diamond, the most important thing to consider is the quality of the diamond. Therefore, at this stage, a diamond grading report or a diamond certificate is an important measure to gain peace of mind.

The most important diamond characteristics that show, graded, and measured the quality of the diamond are the color of the diamond, the clarity of the diamond, the cut of the diamond, and the carat weight. These properties are used to evaluate the diamond and are also called “Four C’s”. These four factors are the properties that have the most influence on the price of the diamond. On the other hand, outside of 4 C, symmetry, light return, polish, fluorescence, etc. features are also included.

USA Diamond certificates usually come from one of three labs. These are the Gemological Institute of America (GIA), American Gem Society (AGS), or European Gemological Laboratory – USA (EGL or EGL USA).

  • GIA, the world’s most famous gemology laboratory, is both the industry’s most reliable and most used laboratory.
  • AGS laboratory is the second most widely used diamond certification laboratory in the world, after the GIA laboratory. AGS has global offices in Israel, India, Belgium, China, and Hong Kong, and AGS is a non-profit, headquartered diamond laboratory in the USA.
  • There is another, more limited diamond laboratory, called the European Gemology Laboratory – USA (EGL or EGL USA).
  • IGI is the only international certification laboratory controlled by a single central governing body, connected to an internationally recognized system for diamond grading.

The quality of a diamond is measured by 4Cs and the diamond rating agency, and among all diamond certifications, AGS and GIA are the most respected and trusted in the industry.


As we mentioned above, a GIA is an acronym that diamond vendors use to describe GIA-rated diamonds. GIA is both a non-profit organization and an independent organization that researches jewelry, trains jewelry professionals, and sets standards for determining diamond quality. The main function of GIA is the grading of diamonds. The GIA created the diamond quality standard, consisting of color, clarity, cut, and carat weight, with scientific procedures for evaluating each “C” and grading terminology used to describe them.

You should know that GIA does not mine diamonds. GIA does not sell, buy, or barter diamonds. It also does not evaluate diamonds and is otherwise not included in diamond pricing or valuation. GIA operates independently of these commercial interests, and due to its nonprofit diamond quality assessments is completely objective and unbiased. If you want to know the quality of the diamond you want to buy, you should look for GIA-grade diamonds and the GIA diamond grading reports to accompany them.

AGS stands for the American Gemological Society and is also a US-based laboratory with headquarters in Las Vegas. The AGS lab is known for its scientific approach and research in diamond cut grading. AGS does not use an alphabetical rating system. Instead, they use a scale from 0 to 10, with 0 being the best and 10 the worst, to rate the properties of a diamond.

Like the GIA, AGS is known for its adherence to ethical standards and consistency in the grading system. The second most widely used laboratory service in the US market after GIA is the AGS laboratory. It also has offices in Israel, Belgium, India, China, and Hong Kong and is therefore consolidated globally. First-time users may find it difficult to understand the AGS methodology, but the methodology is quite simple. It can be quite understandable compared to GIA. For example, if a jeweler informs you that a diamond has an AGS cut grade of 0, a sharpness grade of 3, and a color grade of 2.5, the equivalent of this diamond on the GIA scale can be said to be a perfect cut, and I color diamond with VS1 clarity.

AGS evaluates cut quality based on a more stringent standard compared to GIA. There is a robust optical ray tracing assessment that measures the performance of light of a diamond at the center of the AGS’s cut grading system. In the industry, well-cut super ideal diamonds are sent to AGS instead of GIA. This is because AGS is where “the wheat has separated from the chaff”. The AGS cut grading system is much more advanced and less forgiving when evaluating the craftsmanship of a diamond and performance.

Although GIA is a leading diamond laboratory in the industry, AGS is not far behind. However, an AGS certificate is generally considered far superior to an EGL certificate, which is known to be more flexible than GIA or AGS and often reports higher grades for the same diamond. This is why many consumers feel safer when purchasing GIA or AGS certified diamonds because GIA and AGS, unlike EGL, are non-profit organizations.

Diamond certificates differ between institutions due to differences in professional opinion, rating systems, and naming. The AGS diamond grading is not the same as GIA and EGL. Unlike GIA and EGL, which use alphabetic diamond grading systems, the AGS diamond grading uses a scale from 0 to 10, with 0 for the best and 10 for the worst.

GIA and EGL treat diamond color in alphabetical subdivisions in three broad categories: colorless (grades D, E, F), almost colorless (G, H, I, J), and distinct color (K to Z). However, since color grades are an educated opinion that describes the amount of color present for a diamond when laboratories do not agree on where a color grade should fall, the difference in grading occurs.

There is only one difference between AGS and GIA. This difference is the parameters used to measure the cut quality. AGS cut grading scale is between 0-10. While 0 means Ideal, 8-10 means Poor. On the other hand, the GIA scale includes Excellent, Very Good, Good, Fair, and Poor. Any diamond rated for Cutting by the GIA or AGS is safe and valid. Both GIA and AGS serve to show whether a diamond has a quality cut. Apart from the cut, the remaining grades graded by GIA or AGS overlap depending on how they evaluate the diamond component.


EGL is the abbreviation for the European Gemology Laboratory. EGL, a Europe-based rating agency, has a comprehensive global presence with centers in London, Paris, Tel Aviv, Tokyo, and Johannesburg. EGL is known for pioneering diamond grading techniques even for gems lighter than one carat. At the same time, EGL has a large market share in Europe. It is also famous for the introduction of the “SI3” clarity rating for diamonds.

IGI is the International Gemological Institute in Antwerp, Belgium. It is the second most famous laboratory in the world after the GIA. IGI is a common laboratory in Asian countries that grades significant amounts of polished diamonds on the market. IGI also rates synthetic diamonds on a commercial scale. Although EGL and IGI are more widely known in Europe and Asia, both laboratories have offices in an important city like New York.

How to Grade Diamond Color?

As a general rule, the whitest diamonds are the most expensive, with exceptions such as extremely rare colors such as pink or blue. Diamonds did not consist of pure carbon during their natural formation billions of years ago. One of the main reasons for the color that has the potential to be so different in diamonds is Nitrogen and this is the reason why it has different colors. Apart from that, the overwhelming majority of diamonds range from white (the most expensive) to dark brown or black diamonds (the cheapest).

Many people consider diamonds to be colorless, but most diamonds used in jewelry can be slightly yellow or brown tones. The colorless and rare “fancy-colored” diamonds (blue, pink, orange, green, yellow, or brown) are the most valuable. All other diamonds are graded according to how distinct the color is. The GIA Color Scale ranges from the letter D (colorless) to Z (light yellow). Gemologists use a diamond color master set to compare colors.

From an objective scientific point of view, the whitest diamonds are one of the two fundamentals that make a diamond as pure as possible. Another factor is clarity. The most precious diamonds are the whitest diamonds, and only the highest 20% are sold as jewelry-grade in high-end stores. There is a diamond color grading chart listed from the whitest and most expensive to the yellowest and cheapest.

Grading Colorless Diamonds

According to most diamond experts and jewelers, it is recommended to set diamonds that are colorless in white gold or platinum because yellow gold does not make your colorless diamonds appear as white as they do, which causes more reflection in colorless diamonds than white gold. Most jewelers view using yellow gold in white diamonds as a potential loss and choose to display their higher quality diamonds in either white gold or platinum.

D Grade: In terms of color, the highest quality is the most valuable D color diamond. For an outside eye, it’s not easy to spot the differences between colors D, E, and F, but like any other color, the only way to be sure of this is with a certificate. D-colored diamonds are considered “colorless diamonds” and are the most colorless quality diamonds.

E Grade: It is a grade E diamond, the second-highest quality, and also the second most valuable color grade. As mentioned above, some can be confused with D or F. To guarantee the quality of an E-class diamond, a specialist or certification is required. E-colored diamonds are the second most colorless diamonds and are still considered “colorless diamonds”.

F Grade: The third highest quality color grade and also the third most valuable F grade diamond in terms of color. Only by a trained jeweler can distinguish an F-color diamond from a D-color or E-color diamond. Considered “colorless diamonds” Color F diamonds are considered the third most colorless diamonds.

Grading Near Colorless Diamonds

G-H Grades: Near Colorless diamonds are still very difficult to distinguish, but someone with an average knowledge of diamonds should be able to see a yellow hue. Most people do not differentiate between Near Colorless and Near Colorless Tinted.

Grading Near Colorless Slightly Tinted Diamonds

I-J Grades: I-colored diamonds where yellow marks begin to appear but are still difficult to distinguish from other diamonds of similar color, is described by some as Near Colorless and others as Light Tone Near Colorless. At this stage, it is obvious that while the diamond looks relatively white, the diamond is not very white. Likewise, J-colored diamonds are in the “Nearly Colorless” range on the color scale. Although these diamonds exhibit some hints of color, they still appear essentially colorless when viewed with the naked eye.

Grading Faint Yellow Diamonds

K-M Grades: Diamonds of this grade are faint yellow diamonds and vary in different degrees from K, L to M. This range of colors has a very light yellow appearance that can be distinguished by all under suitable light. On the other hand, although this color is still light, at this point everyone agrees that this color is no longer white.

Grading Very Light Yellow Diamonds

N-R Grades: This range includes N, O, P, Q, R color grades. At this stage, a very clear but very obvious yellow begins to develop but is still significantly whiter than yellow. Due to the high likelihood of customers being dissatisfied, most jewelers and diamond sellers choose not to mess around with this range anymore and sell diamonds in this range.

Grading Light Yellow Diamonds

S-Z Grades: Light Yellow Diamonds consist of S, T, U, V, W, X, Y, and Z grades and at this point, yellow is highly distinguishable. However, it is still relatively light in color, but people consider this color to be visually unattractive and therefore prefer a lighter color or a fancy color by standards.

Grading Yellow Diamonds

Fancy: Diamonds can come in many colors, but once they have a true yellow color they can no longer be categorized under the normal system, they have a separate and own system. Fancy colored diamonds can range from yellow to dark brown and even almost black. These diamonds also appear in light blue and pink colors, but this is very rare.

How to Grade Diamond Clarity?

The clarity of a diamond is a factor that largely determines the price of a diamond. Clarity refers to the absence of inclusions (internal features) and imperfections (external features). Natural diamonds are formed when carbon is exposed to high degrees of heat and pressure, leading to the formation of residues and defects. There are a few things to look for when assessing clarity, all of which affect the overall appearance of the diamond. The rarest diamonds, and therefore the most valuable and most special, are those with the fewest possible inclusions.

The natural factors that lead to the formation of diamonds are enormous heat and pressure. For this reason, a diamond can have internal and external features that affect its clarity. Features that are internally formed are called inclusion; on the other hand, features that externally form are called blemishes. Gemologists use these properties to rate the grade of diamonds’ clarity and there are 11 grades shown. The first grade is “Flawless” and the last grade is “Included” on the internationally recognized GIA scale.

Internal features are called “inclusion”; external features are called “blemishes”. These properties are used by gemologists to rate the clarity of diamonds, and there are 11 grades from “Flawless” to “Included” on the internationally recognized GIA scale.

Grading Internally Flawless Diamonds

FL-IF Grades: This grade is the Flawless (FL) grade with no inclusions or blemishes even under ten times magnification. Flawless diamonds are expensive due to their rarity. Internally Flawless diamonds contain no residue but are rather minor blemishes that a specialist can see under ten times magnification. “Internally Flawless” diamonds are still very rare and only the top 2% puts it in this category and therefore has a true gem rating.

Grading Very Very Slightly Included Diamonds

VVS1-VVS2 Grades: This category consists of the Very Very Slightly Included 1 (VVS1) and Very Slightly Included 2 (VVS2) ratings. As the name suggests, VVS1 is one rating better than VVS2. When you magnify them ten times, the amount of inclusions is less, but of course, an expert can see them with some difficulty. These diamonds are top-level diamonds, making up only 1 out of 12 diamonds, and this grade is ideal for a fine gem.

Grading Very Slightly Included Diamonds

VS1-VS2 Grades: This grade consists of “Very Slightly Included 1” (VS1) and “Very Slightly Included 2” (VS2) grades. This class of diamond is still well suited for a gem. This is because only one-sixth is equal to or greater than a diamond. Therefore, the VS1 and VS2 are still very high quality, they are still relatively expensive diamonds.

Grading Slightly Included Diamonds

SI1-SI2 Grades: It is of SI1 and SI2 clarity where diamonds begin to show obvious inclusions that can be easily seen under magnification. Almost a third of diamonds make up this grade or higher, making this grade quite common. At this point, this degree is the breaking point when many jewelers choose clarity for a gem. In this case, consumers make a choice; they either prefer a higher quality or, as a minimum, agree to it.

Grading Diamonds with Obvious Inclusions

I1 Grade: A diamond of this grade has large inclusions that can be seen with the naked eye. The lower half of all diamonds mined are of this grade. I1 colored diamonds should not be used in fine jewelry.

Grading Diamonds with Very Obvious Inclusions

I2-I3 Grades: Located at the lower end of the lower half in terms of rarity, this diamond quality not only has inclusions visible to the naked eye but also begins to prevent the diamond from reflecting light. Most people would not think of buying a diamond with such a sharpness rating and almost every diamond expert and jeweler advises their customers not to buy such a stone.

How to Grade Diamond Carat?

The word “carat” has an interesting origin. The term comes from a 10-meter tall tree called “Ceratonia Siliqua” and the tree produces a fruit that continuously forms a pit weighing 0.2 grams. Since there is an extraordinary consistency in their weight, they have been used to measure diamonds for over a thousand years, and even today the unit of measurement reached with this tree.

An uncut and rough diamond is usually much heavier than a cut diamond. For example, a diamond typically loses 50-60% of its weight before it reaches its final polished version. A stone of the same quality will cost a higher price when it weighs more carats. It is also worth noting that diamond prices increase with the snowball effect when they get heavier in carats because these diamonds become increasingly and disproportionately difficult to find.

How to Grade Diamond Cut?

Cut refers to the shape of the diamond, but it is expressed in how well the facets interact with light. Grading cuts are hard work and are important in determining the value. The cut type of a diamond determines how the diamond shape compares to its standard proportions. The reason why diamond cuts are not ideal is that experts determine that they have the best balance between size and ratio during the examination of the stone. It is the ideal cut that brings out the best in a diamond, and a high-quality cut brings out the true beauty of a diamond.

The cut grade is one of four evaluation criteria determined under the GIA Cut Grading System to demonstrate the overall cut quality for a round cut diamond. Concerning to a diamond with a cut degree applied, some looks and proportions should be considered before the finishing stage. The criteria considered by gemologists to reveal the final cut degree take into account symmetry, finish, and culet.

Another thing made possible by the GIA Cut Grading System is that the industry formed within the framework of a precious stone, diamond, can use the color, clarity, and carat weight of the diamond together with the cut in the process of evaluating or buying a diamond.

Excellent: Excellent cut diamonds are perfect for standard ideals or quite close to perfection. This is the cut quality most recommended by diamond experts and jewelers. About 1 out of 25 diamonds are cut according to this standard. This is the best light cut where about 1 out of 25 diamonds are cut to this standard.

Very Good: The second best cut variety, the difference is hardly distinguishable but the amount of light entering the diamond is affected negatively slightly. About 1 in 8 diamonds are cut to this standard.

Good:  Although the difference between good cut diamonds, which is the second-best cut type, and an excellent cut is not noticeable, the amount of light entering the diamond is negatively affected. About 1 out of 8 diamonds are cut according to this standard. 

Fair: At this point, the cut begins to deviate significantly from the standard and the luminosity is significantly adversely affected. It is generally not recommended to buy diamonds of this quality.

Poor: In this degree cut, the shine, shape, and faces of the diamond are heavily affected. Buying diamonds of this variety is not highly recommended.

This image provides a good visual representation that imperfect cuts will cause an imperfect reflection of light within the diamond and highlights the importance of cut quality. Therefore, it is recommended that the diamond cut quality be as close to ideal as possible before purchasing a diamond.

A visual representation of Cut Quality and their outcomes in the light reflection of the diamond as follows:

Round Brilliant Cut: The Ideal Cut

The brilliance of a diamond is measured by the quality of its cut. Types of cuts for the round cut are as follows:

Ideal Cut: An ideal cut diamond that allows light to reflect across the table and crown gives the diamond fire, shine, and plenty of sparkles. 

Deep Cut: A deep-cut diamond is a cut in which light seeps from below, causing the diamond to appear dull and lifeless.

Shallow Cut: A shallow cut diamond is the type of cut that causes light to leak from the edges and the diamond to lose its shine.

Do You Need to Get a Diamond Graded?

If you want to buy a diamond engagement or wedding ring, you should know that you will make a very important choice and also this ring can be one of the most expensive rings. Therefore, you will want to make sure you get a good value and quality for the diamond in mind. In this case, a GIA diamond grading report gives you all the important information you need to know about a diamond’s 4Cs, fluorescence, any process, and more. The GIA diamond grading report ensures that your diamond is natural because the GIA examines and tests the diamond using the most advanced tools and procedures available, with the information provided by the Institute’s ongoing scientific research.

The GIA diamond grading report objectively evaluates the quality characteristics of the stone and allows you to compare a GIA-rated diamond with another diamond. In this direction, the quality of loose diamonds is compared and allows you to decide which one is the most suitable and right for you. Making sure a diamond comes with a GIA diamond rating report is similar to having an independent review before buying a car or home. This is a smart step in your purchasing process, and most insurance companies need a GIA rating report when you have your diamond insured.

Do “GIA Certified” Diamonds Cost More?

The term “GIA certified” is an inaccurate name for GIA-grade diamonds, and there is often a misconception that GIA diamonds are more expensive, based on comparing diamonds based solely on the price tag. The price of a diamond, car, or other precious item depends on its quality. If you are unsure of this quality, how do you realize that you have overpaid or are getting a good deal? Therefore, you should compare the prices of diamonds with the same 4C quality characteristics and whose properties have been accurately and objectively graded by an independent laboratory, like GIA.

Having a GIA-rated diamond does not mean you will spend a lot of money. The GIA charges as low as $ 48 for the rating report for a diamond weighing 0.70 ct to 0.99 ct, and as low as $ 80 for a diamond between 1.00 ct to 1.49 ct. Although you may not know this, most jewelers add their rating fees to the diamond product price. For example, given that people paid an average of $ 6,351 for an engagement ring in 2017, you should know that the cost of the GIA diamond rating report is a small price you can confidently pay.


Besides the 4 C’s, an AGS report also provides information on the width, depth, and table size of a diamond.

Diamond Width

The width of a diamond is characterized as the length from one end of its girdle, that is, its diameter at its widest point, to the other end of the girdle, and determines the proportionality of the stone. When it comes to calculating the length-to-width ratio of a diamond, the width is a very important factor.


The height of the diamond from the culet to the top of the table is defined as the percentage of depth, and this is determined by the depth divided by the width. This measurement is reported in millimeters and percent. For example, for a diamond 4mm deep and 4.5mm wide, the percentage of depth is determined as 88.8%. A lower depth percentage of two equal carat diamonds usually appear larger due to the increased width. However, a very low percentage of depth may cause a dark appearance because it does not reflect light very well.

Table Size

To calculate the diamond table% is divided by the area of the upper surface i.e. the width and diameter of the table. The table is 70% when the table face is 3.5mm wide and diamond 5mm wide. An ideal table percentage differs according to the shape of the diamond, and you should seek professional help to determine if a diamond has a high-quality table percentage.

Upgrade Shopping

The only thing to be aware of is “upgrading the shopping”. Objective grades such as color and sharpness, weight, and size are altered and therefore no laboratory can qualify as 100% accurate.

If there is a diamond somewhere between the grades, a manufacturer or retailer can choose to ship the diamond to multiple laboratories looking for better quality. For example, suppose a diamond has the characteristics of I color or J color and receives a J color from GIA.

The wholesaler or retailer can try to send it to AGS for the I color and then sell it for much more money. Although the grades are much more likely to be the same, they can get the upgrade and this will greatly compensate for the cost of sending it to AGS for certification. Companies widely use AGS for branded super ideal diamonds. However, it is not widely used for non-round diamonds. Advantages of AGS Certification as follows:

  • It is a highly reputable certificate.
  • It offers a reliable and consistent rating.
  • It allows you to reach the diamond quality specified by the certificate.
  • Provides security measures to help ensure authenticity

Disadvantages of AGS Certification as follows:

  • Be careful with upgrades

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Savaş Ateş

My wife has a huge interest in diamonds. After she asked me a lot of questions about it, I found myself in diamonds. I made a lot of research on it. I read books. I visited manufacturers. I visited the stores. I have made good friends in that field. I want to share my experiences with you.

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