The 4 C’s of Diamond, Carat, Cut, Color, Clarity is a system developed by the Gemological Institute of America many years ago. The American Gem Society uses a very similar system to evaluate diamonds using a 0-10 scale. These two organizations have always been the utmost authorities on diamond evaluation since their inception. Summaries are listed below from their websites, for Gemological Institute of America, and for American Gem Society. These four factors will help determine the value of a particular diamond. If you have any questions about the 4 Cs of Diamonds, please contact us, we would love to clarify these diamond grading standards with you.

From the Gemological Institute of America’s website

About the 4Cs

Because diamonds are so valuable, it’s essential to have a universal grading system for comparing their quality. In the 1940s and ’50s, GIA developed the 4Cs and the GIA International Diamond Grading System™ to objectively compare and evaluate diamonds.

  • Carat
  • Color
  • Clarity
  • Cut


Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. (Don’t confuse carat with karat, as in “18K gold,” which refers to gold purity.)

Just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, color and cut. The majority of diamonds used in fine jewelry weigh one carat or less.

Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. In the diamond industry, weight is often measured to the hundred thousandths of a carat, and rounded to a  hundredth of a carat.  Diamond weights greater than one carat are expressed in carats and decimals. (For instance, a 1.08 ct. stone would be described as “one point oh eight carats,” or “one oh eight.”)

How did the carat system start?

The carat, the standard unit of weight for diamonds and other gemstones, takes its name from the carob seed. Because these small seeds had a fairly uniform weight, early gem traders used them as counterweights in their balance scales. The modern metric carat, equal to 0.2 grams, was adopted by the United States in 1913 and other countries soon after. Today, a carat weighs exactly the same in every corner of the world.


Diamond color is all about what you can’t see. Diamonds are valued by how closely they approach colorlessness – the less color, the higher their value. (The exception to this is fancy-color diamonds, such as pinks and blues, which lie outside this color range.)

Most diamonds found in jewelry stores run from colorless to near-colorless, with slight hints of yellow or brown.

GIA’s color-grading scale for diamonds is the industry standard. The scale begins with the letter D, representing colorless, and continues with increasing presence of color to the letter Z, or near-colorless. Each letter grade has a clearly defined range of color appearance. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.

Many of these color distinctions are so subtle as to be invisible to the untrained eye. But these slight differences make a very big difference in diamond quality and price.

Why does the GIA color grading system start at D?

Before GIA developed the D-Z Color Grading Scale, a variety of other systems were loosely applied. These included letters of the alphabet (A, B and C, with multiple A’s for the best stones), Arabic (0, 1, 2, 3) and Roman (I, II, III) numerals, and descriptions such as “gem blue” or “blue white.” The result of all these grading systems was inconsistency and inaccuracy. Because the creators of the GIA Color Scale wanted to start fresh, without any association with earlier systems, they chose to start with the letter D—a letter grade normally not associated with top quality.


Because diamonds formed deep within the earth, under extreme heat and pressure, they often contain unique birthmarks, either internal (inclusions) or external (blemishes).

Diamond clarity refers to the absence of these inclusions and blemishes. Diamonds without these birthmarks are rare, and rarity affects a diamond’s value. Using the GIA International Diamond Grading System™, diamonds are assigned a clarity grade that ranges from flawless (FL) to diamonds with obvious  inclusions (I3).

Every diamond is unique. None is absolutely perfect under 10× magnification, though some come close. Known as Flawless diamonds, these are exceptionally rare. Most jewelers have never even seen one.

The GIA Clarity Scale contains 11 grades, with most diamonds falling into the VS (very slightly included) or SI (slightly included) categories. In determining a clarity grade, the GIA system considers the size, nature, position, color or relief, and quantity of clarity characteristics visible under 10× magnification.

Flawless (FL) – No inclusions or blemishes are visible to a skilled grader using 10× magnification
Internally Flawless (IF) – No inclusions and only blemishes are visible to a skilled grader using 10× magnification
Very, Very Slightly Included (VVS1 and VVS2) – Inclusions are difficult for a skilled grader to see under 10× magnification
Very Slightly Included (VS1 and VS2) – Inclusions are clearly visible under 10× magnification but can be characterized as minor
Slightly Included (SI1 and SI2) – Inclusions are noticeable to a skilled grader using 10× magnification
Included (I1, I2, and I3) – Inclusions are obvious under 10× magnification and may affect transparency and brilliance

How did the GIA Clarity Scale come about?

Like the color scale, GIA’s clarity grading system developed because jewelers were using terms that were easily misinterpreted, such as “loupe clean,” or “piqué.” Today, even if you buy a diamond in another part of the world, the jeweler will likely use terms such as VVS1 or SI2, even if her language is French or Japanese instead of English.


Cut is the factor that fuels a diamond’s fire, sparkle and brilliance.

The traditional 58 facets in a round brilliant diamond, each precisely cut and defined, are as small as two millimeters in diameter. But without this precision, a diamond wouldn’t be nearly as beautiful. The allure of a particular diamond depends more on cut than anything else.

Though extremely difficult to analyze or quantify, the cut of any diamond has three attributes: brilliance (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the flashes of light, or sparkle, when a diamond is moved).

An understanding of diamond cut begins with the shape of a diamond. The standard round brilliant is the shape used in most diamond jewelry. All others are known as fancy shapes. Traditional fancy shapes include the marquise, pear, oval and emerald cuts. Hearts, cushions, triangles and a variety of others are also gaining popularity in diamond jewelry.

As a value factor, though, cut refers to a diamond’s proportions, symmetry and polish. For example, look at a side view of the standard round brilliant. The major components, from top to bottom, are the crown, girdle and pavilion. A round brilliant cut diamond has 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion that’s known as the culet. The large, flat facet on the top is the table. The proportions of a diamond refer to the relationships between table size, crown angle and pavilion depth. A wide range of proportion combinations are possible, and these ultimately affect the stone’s interaction with light.

In early 2005, GIA unveiled a diamond cut grading system for standard round brilliants in the D-to-Z color range. This system, the product of more than 15 years of intensive research and testing, assigns an overall diamond cut grade ranging from Excellent, Very Good, Good, Fair, and Poor.

How does pavilion depth affect a diamond’s cut?

The distance from the bottom of the girdle to the culet is the pavilion depth. A pavilion depth that’s too shallow or too deep will allow light to escape through the sides or the bottom of the stone. A well-cut diamond will direct more light through the crown.

From the American Gem Society’s website

Taking the Guesswork Out of Diamond Buying

Most people know little about diamonds.  That’s why the American Gem Society came into existence over 70 years ago.  Thanks to Society members, we now have precise standards for evaluating diamonds, commonly known as the 4 Cs: Cut, Color, Clarity, and Carat Weight.  The American Gem Society Diamond Grading Standards evaluate three of the four value factors — cut, color, and clarity — on its own 0 –10 scale.  0 (Zero) is the highest grade, and 10 is the lowest.  AGS “0” indicates an AGS Ideal Cut diamond that has no color and no inclusions or internal characteristics.  The three factors are expressed separately along with the fourth factor, the carat weight of the gemstone, for the final American Gem Society Grade.

The Science of Diamonds

While not everyone will share the same opinion as to what constitutes beauty, most people want a diamond that expresses their individual taste and personality. Here’s what you should consider first, however, before buying a diamond:

Cut. Of all the 4 Cs, cut has the greatest effect on a diamond’s beauty.  In grading, cut evaluates the cutters skill in the fashioning of the diamond.

Diamonds have a unique ability to manipulate light efficiently. This unique ability can be released and maximized only by cutting and polishing the diamond to an extremely high level of accuracy. The American Gem Society Cut Grading Systemconsiders not only the proportions of a diamond, but also the craftsmanship of its overall symmetry and polish. It is unique in that it uses the latest in technology to analyze the cut’s impact on the diamond’s light performance.

Color. A truly colorless diamond is extremely rare.  Most diamonds possess varying degrees of yellow or brown and small, subtle differences in color can make a substantial difference in value. If a diamond is well cut, the diamond’s refraction and dispersion often will disguise certain degrees of coloration. Unless a diamond is a fancy color (or any color other than colorless to light yellow or brown), the American Gem Society Color Grading System places it on a 0 to 10 scale, 0 being colorless. To accurately and consistently grade color, an American Gem Society experienced grader will utilize special lighting to compare the diamond being graded to a set of American Gem Society Master Color Comparison Diamonds, which have met exacting standards of cut, color, clarity, and carat weight.

Clarity. Clarity is the evaluation of a diamond’s internal and external characteristics. The fewer inclusions or blemishes, the more desirable the diamond. Inclusions are internal, that is, inside the diamond. Crystals are merely minerals trapped inside the diamond; feathers are breaks in the diamond. Blemishes are usually very small and are only on the surface of diamonds. To locate these tiny characteristics, an American Gem Society member jeweler will use a binocular microscope that magnifies the diamond ten times. Then, evaluating the size, location, nature, number, and color of all the inclusions and blemishes, a clarity grade from 0-10 is assigned – 0 being flawless or internally flawless.

Carat. The standard used to measure diamond weight is the carat.  A carat equals 1/5 of a gram (or 1/142 of an ounce).  Each carat is further divided into points, each point representing 1/100th of a carat. While weight may be the least important of the four Cs in determining value, it may be the easiest of the four Cs to gauge accurately and is the most objective. As diamonds increase in size, their cost tends to increase geometrically. Thus, a one-carat diamond may cost more than twice as much as a one-half carat stone of equal quality. Also, as previously stated, weight does not always enhance the value of a diamond. In fact, when a diamond is improperly cut, added weight may serve only to reduce its brilliance. For these reasons, you should consult with an American Gem Society titleholder regarding the question of carat weight.