A diamond grading report contains a wealth of information, and understanding every field will help you evaluate diamonds with confidence. Whether you are reading a GIA, AGS, or IGI report, the core information is similar. Here is what each section means.
Report Header Information
Report Number: A unique identification number assigned to this specific diamond. Use this number to verify the report online through the issuing lab's website (GIA: gia.edu, AGS: ags.org, IGI: igi.org). Always verify before purchasing.
Date: When the report was issued. Diamond characteristics do not change over time under normal circumstances, so an older report is not inherently less reliable. However, a very old report (10+ years) on an expensive diamond may warrant re-certification to confirm no damage has occurred.
Shape and Cutting Style: The diamond's shape (round brilliant, princess, oval, etc.) and faceting pattern. "Modified brilliant" indicates a fancy shape using a variation of the round brilliant faceting pattern.
The 4Cs Section
Carat Weight: The diamond's weight measured to the hundredth of a carat. One carat equals 0.2 grams. This is the most objective measurement on the report — it is simply a weight reading from a calibrated electronic scale.
Color Grade: On the D-to-Z scale, this indicates how much body color the diamond exhibits. D-F are colorless, G-J are near-colorless, and K+ shows increasingly noticeable yellow or brown tint.
Clarity Grade: From FL (Flawless) to I3, this indicates the presence and visibility of natural inclusions and blemishes as seen under 10x magnification. VS2 and above are considered "eye-clean" — inclusions are not visible without magnification.
Cut Grade: For round brilliant diamonds, this evaluates how well the diamond's proportions, symmetry, and polish work together to create brilliance, fire, and scintillation. Note: GIA only provides a cut grade for round brilliants. AGS grades cut for all shapes.
Measurements
Dimensions: Listed as minimum diameter – maximum diameter x depth for round diamonds, or length x width x depth for fancy shapes. These measurements are in millimeters. For round diamonds, the closer the minimum and maximum diameters, the more perfectly round the stone is.
Proportions
The proportions section (or diagram) shows the specific measurements that determine how light behaves inside the diamond:
Table Percentage: The width of the flat top facet as a percentage of the total diameter. Ideal range for round brilliant: 54-57%. A table that is too large or too small reduces brilliance.
Depth Percentage: The total height of the diamond as a percentage of its diameter. Ideal range for round brilliant: 59-62.5%. Diamonds that are too deep look smaller face-up because weight is hidden in the depth. Diamonds that are too shallow leak light through the bottom.
Crown Angle: The angle of the crown facets relative to the table. Ideal: 34-35 degrees. This affects the balance between brilliance (white light) and fire (rainbow colors).
Pavilion Angle: The angle of the bottom facets. Ideal: 40.6-41 degrees. This is the single most critical proportion for light return. Even small deviations can significantly reduce brilliance.
Girdle Thickness: The narrow band at the widest part of the diamond. Ranges from Extremely Thin to Extremely Thick. Ideal: Thin to Slightly Thick. An extremely thin girdle is vulnerable to chipping; an extremely thick girdle hides carat weight without adding to face-up size.
Culet: The tiny facet at the very bottom point of the diamond. Ideally None or Very Small. A large culet can be visible through the table as a dark spot.
Additional Grading Details
Polish: Graded Excellent to Poor. Evaluates the smoothness of the diamond's facet surfaces. Surface imperfections from the polishing process can reduce light performance. Excellent or Very Good is recommended.
Symmetry: Graded Excellent to Poor. Evaluates how precisely the facets align and intersect. Poor symmetry can misdirect light and reduce brilliance. Excellent or Very Good is recommended.
Fluorescence: Ranges from None to Very Strong (typically blue). Fluorescence is the diamond's tendency to emit visible light when exposed to ultraviolet light. None to Faint is preferred by most buyers. Medium to Strong Blue fluorescence can sometimes make a diamond appear hazy in certain lighting, but in many cases it has no visible impact and can even improve the appearance of lower-color diamonds (I-J) by making them look whiter.
Clarity Plot
On full grading reports (GIA Diamond Grading Report, not Dossier), you will find a clarity plot — a diagram showing the location, size, and type of inclusions in the diamond. Common inclusion types marked on the plot include:
- Crystal: A mineral crystal trapped inside the diamond (shown as a small dot or shape)
- Feather: A small crack or fracture (shown as a line)
- Cloud: A cluster of tiny pinpoints (shown as a circle of dots)
- Pinpoint: A very tiny inclusion (shown as a single dot)
- Needle: A long, thin inclusion (shown as a line)
- Twinning Wisp: Distorted growth patterns (shown as wavy lines)
Green markings indicate internal inclusions; red markings indicate surface blemishes. The plot helps you understand where the inclusions are located — inclusions near the edge (under prongs once set) are less concerning than those directly under the table.
Security Features
Reputable grading reports include security features to prevent forgery: microprint lines, holographic labels, QR codes, and watermarks. The most reliable verification is always to check the report number directly on the grading lab's website.
Summary: What to Focus On
When evaluating a diamond grading report, focus on these essentials:
- Verify the report number online with the issuing lab
- Check the cut grade — this has the biggest impact on beauty
- Review the clarity and color grades against the price you are paying
- Look at the proportions (especially table %, depth %, and pavilion angle)
- Check fluorescence — None to Faint is safest
- Review the clarity plot to understand where inclusions are located
Armed with this knowledge, you can confidently evaluate any diamond and ensure you are getting exactly what you pay for. Browse certified diamonds at USA Jewels or use our Design Your Own Ring tool.