Diamond Grading Reports Explained

When purchasing diamond jewelry, it is always a good idea to make sure that the diamonds come with a grading report. Diamond grading reports are available from a variety of different grading labs such as the Gemological Institute of America (GIA) or American Gem Society (AGS), as we detailed in this article.

Having a diamond grading report is great, but it is full of technical information that can be confusing for many people. Understanding each part of the report and what it means for your diamond is essential, as it will empower you to make an informed purchase decision.

Report Number

The first thing that you will notice on a diamond grading report is the report number. The report number is a unique identification number assigned to that specific diamond, and is used for reference and tracking. If you receive an appraisal on your jewelry, the report number will be included, and it is also oftentimes engraved on the girdle of the diamond so it can be identified when viewed under magnification. This is important when leaving your jewelry anywhere for repair, as you can identify your diamond upon dropoff and pickup by viewing this number. If for any reason you ever lose your diamond grading report, you can always contact the grading lab and request a duplicate copy if you have your report number.

Diamond Basics

The next items on the grading report are typically the shape, measurements, and carat weight of the diamond. The shape will be noted as round brilliant cut, oval, princess, asscher, pear, marquise, etc. The carat weight of the stone is written as a decimal, for example 1.05ct is just over 1.00 carat–which for many people is the ideal size diamond for an engagement ring. The measurements of the stone will be written in millimeters and will include length, width, and height for fancy shapes or diameter and depth for round diamonds. Diamond proportions are also typically included as percentages on the report and shown with a diagram. Ideal proportions can vary depending upon the shape of your diamond (a topic which can be explored in greater detail in another article). It is important to note that the proportions of the diamond will determine the cut grade, which is listed on the grading report with the color and clarity grade.


The section of the diamond grading report which is usually seen as the most important by consumers is the 4Cs section: cut, color, clarity, and carat weight. The cut, which we just discussed is determined by proportions, can be characterized using different labels, depending upon the grading laboratory used. Some labs have the highest cut grade of “ideal”, while others use “excellent,” but essentially they are the same thing. When evaluating cut grade, you must know the scale the lab is working on to properly understand where your diamond falls on the scale. Carat weight was also previously covered, so let’s focus on color and clarity.

The color grade of a diamond evaluates the presence or absence of color in the diamond. The GIA has created the standard for color grading in the diamond industry and their scale ranges from D (completely colorless) to Z (light yellow or brown). Any diamonds graded D - F are considered to be colorless, and as you work your way down the scale, the diamonds contain more traces of color (usually yellow). That being said, diamonds with some color can be beautiful, especially when set in yellow or rose gold, as their color is just further enhanced by the reflection of the metal within the stone. There are also fancy color diamonds, which have a more intense color and can range from canary yellow to blue and green. These diamonds are graded on a different color scale and can fetch a very high price tag due to how rare they are, especially if they are untreated diamonds.

Diamond clarity is the measure of how clear or flawless a diamond appears when examined under magnification. Diamonds are evaluated to identify small imperfections (inclusions) and external blemishes. The clarity of a diamond is graded on a scale ranging from Flawless (no visible inclusions) to Included (inclusions are visible to the naked eye). Not surprisingly, higher clarity grades typically command higher prices. The location of inclusions is often mapped out on a diamond grading report, along with the type of inclusion so you can identify your diamond specifically compared to others.

Inclusions can come in many forms. Pinpoints are small transparent crystals scattered throughout a diamond, typically having minimal effect on its appearance. Feathers are small fractures within a diamond, resembling tiny feathers, which can vary in size and may or may not be visible to the naked eye. Depending on their size, feathers can affect both the appearance and durability of the diamond. Clouds are clusters of small pinpoints that create a cloudy appearance in the diamond, and the extent of their impact depends on their size. Crystals are small mineral spots within a diamond that can affect its appearance, contingent upon their location and size. Lastly, needles are long, thin crystals resembling needles, usually invisible to the naked eye and therefore not affecting the diamond's appearance unless they are exceptionally large.

Polish & Symmetry

Polish and symmetry are the next items listed on a diamond grading report. These can both be graded on a scale from “excellent” to “poor.” Both of these aspects also influence the cut grade assigned to the diamond. The polish of a diamond refers to the quality of the surface. A well-polished diamond has a smooth surface that allows light to pass through, increasing the sparkle. In contrast, a poorly polished diamond will appear dull and have very little light refraction. Symmetry relates to the alignment of the diamond facets. When a diamond has excellent symmetry, the facets effectively reflect the light passing through the stone to create the most sparkle possible.


Fluorescence is another important factor to consider when reading a diamond grading certificate. A diamond with fluorescence will glow when exposed to UV light. To many people, this isn’t particularly important, as the diamond will really only glow brightly under specific conditions, such as at a club with black lights, etc. This is a desirable trait for some people, as well! It can slightly affect the color of the diamond under sunlight, as the diamond can look just a bit brighter/whiter than it usually would. A diamond with strong fluorescence can sometimes look cloudy in sunlight. It is evident in approximately 30% of diamonds and while it can affect the price of a diamond, it’s not a significant difference since it depends upon the individual customer if they prefer to have a diamond with fluorescence or not.

When purchasing diamond jewelry, ensuring that it has a diamond grading report from a reputable lab is recommended. Although on the surface, a grading report can seem overly technical and confusing, once each part is explained, it can be very easy to interpret. Now that you understand each individual section of the report and what it means, you’ll be able to evaluate the diamond and make an informed decision about the jewelry that you are purchasing. Since grading reports provide insight into individual characteristics about each diamond, understanding what each aspect means and how it can affect the durability and pricing of the diamond is paramount to making a smart purchase.