A grading report packs a lot into one page. Most of it is precise and useful, as long as you know which lines describe the stone and which describe the paperwork.
A diamond grading report from an independent laboratory is the closest thing a diamond has to a passport. It records what the lab measured and observed on a particular day, in a standard format that makes stones comparable. The layout varies a little between labs and report types, but the sections below appear on most full reports for natural diamonds.
Report number, date and verification
Every report has a unique number and an issue date. Before relying on a report, look the number up on the issuing lab’s website to confirm it is genuine and that the details match. Many reports also note a laser inscription, a tiny number written on the stone’s girdle (its thin outer edge). With a jeweler’s loupe you can check that the inscription matches the report.
The report describes the stone at the time of grading. If a diamond has since been chipped, recut or treated, the report no longer describes it accurately.
Shape, cutting style and measurements
“Round brilliant,” “oval modified brilliant” or “emerald cut” identifies the shape and facet style. Our comparison of diamond shapes explains the terms.
Measurements come in millimeters. For rounds they are written as minimum diameter, maximum diameter and depth; for other shapes as length, width and depth. These numbers matter more than they first appear: two stones of the same carat weight can look noticeably different in size face-up if one carries more weight in its depth. For elongated shapes, divide length by width to get the ratio covered in length-to-width ratio and the bow-tie effect.
The grading results
| Line | What it means | Typical scale |
|---|---|---|
| Carat weight | Weight, where 1 carat equals 0.2 grams | Two decimal places |
| Color grade | How colorless the stone is | D (colorless) to Z (light yellow or brown) |
| Clarity grade | Size, number and visibility of inclusions under 10x magnification | FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, I3 |
| Cut grade | Overall cut quality, for standard round brilliants | Excellent, Very Good, Good, Fair, Poor |
| Polish | Smoothness of the facet surfaces | Excellent to Poor |
| Symmetry | Precision of facet shape and alignment | Excellent to Poor |
| Fluorescence | Glow under ultraviolet light | None, Faint, Medium, Strong, Very Strong |
Most labs do not give fancy shapes an overall cut grade, so for ovals, cushions or emeralds you rely more on polish, symmetry, proportions and images. Fluorescence is explained in our guide to diamond fluorescence.
Clarity characteristics and the plot
Full reports include a diagram of the stone with its main inclusions marked by symbols, plus a key listing them, such as crystal, feather, needle or cloud. Two stones with the same clarity grade can look quite different. Use the plot to check:
- Where inclusions sit. Inclusions near the edge can often be hidden under a prong, while one in the center of the table is harder to hide.
- What type they are. Feathers are small fractures. A large feather near the girdle deserves a closer look, because it is the kind of inclusion most likely to matter for durability.
- How many there are. A long list at a high clarity grade usually means many tiny, faint features.
Smaller diamonds are sometimes graded on a shorter report without a full plot. That is normal, but you then rely more on photos and videos.
Proportions diagram
The proportions diagram gives table size, total depth, crown and pavilion angles, girdle thickness and culet size. You do not need to memorize ideal numbers. What helps is comparing stones of the same shape: very deep stones look smaller for their weight, and very thin girdles are more prone to chipping. For step cuts, see emerald and Asscher cuts.
Comments
The comments line catches what the grades do not. Common examples include clouds that are not shown on the plot, surface graining, additional inscriptions and notes about treatment. Any treatment must be disclosed, as covered in gemstone treatments. Read this line every time.
Remember this: Grading standards are applied by people and instruments, and labs differ in reputation and consistency. Comparing stones graded by the same lab is the fairest comparison. Our overview of grading labs explains the differences.
What a report does not tell you
A report says nothing about price, how a stone looks in a particular setting or whether the cutting gives a bow-tie in an elongated shape. It also does not cover the metal or small side stones. Treat it as a reliable description of the center stone, then judge the rest with your own eyes, photos and videos.
Quick notes
- Check that the report number can be verified on the lab’s website and, if the stone is inscribed, that the inscription matches.
- Measurements in millimeters tell you how large the stone looks face-up, which carat weight alone does not.
- Overall cut grades are only given to standard round brilliants; for other shapes, polish, symmetry and proportions carry more weight.
- The comments line and the clarity plot often explain more about a stone than the clarity grade itself.
Common questions
Q: Is a grading report the same as an appraisal?
A: No. A grading report describes the stone’s characteristics without assigning a money value. An appraisal estimates value, usually for insurance, and is prepared by an appraiser rather than a grading lab.
Q: How do I know a report belongs to the diamond I am buying?
A: Look up the report number on the lab’s website, compare the measurements and weight with the stone, and check the laser inscription on the girdle with a loupe if the report lists one.
Q: Do lab-grown diamonds get the same report?
A: Labs issue separate report types for laboratory-grown diamonds, and the format and grading terms can differ from natural diamond reports. The report should state clearly that the stone is laboratory-grown.
Q: What does a comment like ‘clouds are not shown’ mean?
A: It means the stone contains tiny clusters of inclusions that are too small or too numerous to draw on the plot. Most are harmless, but large clouds can affect transparency, so photos or an in-person look help.