How to Read a GIA Diamond Report: A Buyer's Guide
When you buy a loose natural diamond, the stone and its report travel together. The Gemological Institute of America (GIA) grades diamonds independently. It does not buy or sell stones, so its report tells you what the diamond is. Here is how to read one in a few minutes.
1. Report number and date
Every GIA report has a unique number. On many stones, the same number is laser-inscribed on the girdle (the thin outer edge) and can be seen under magnification. This number is your key to verifying the report online.
2. Shape and cutting style
For example, "Round Brilliant", "Oval Modified Brilliant" or "Pear Brilliant". This describes the outline and the facet pattern.
3. Measurements
The stone's size in millimetres. Two diamonds of the same carat weight can look different in size, so measurements tell you how big the stone will actually look.
4. The 4Cs
Carat weight: the diamond's weight, recorded to two decimal places. One carat is 0.20 grams.
Colour: graded from D (colourless) to Z (light yellow or brown). D, E and F are the colourless grades.
Clarity: how free the stone is from inclusions and blemishes. The scale runs FL (Flawless), IF, VVS1, VVS2, VS1, VS2, SI1, SI2, then I1 to I3.
Cut: for standard round brilliants, GIA gives an overall cut grade from Excellent to Poor. Cut has the biggest effect on how much a diamond sparkles.
5. Polish, symmetry and fluorescence
Polish and symmetry describe the finish of the facets, graded Excellent to Poor. Fluorescence describes how the stone reacts to ultraviolet light, from None to Very Strong. It is not a fault in itself, but it can affect appearance and value, so it is worth asking about.
6. The plot and proportions diagram
The plot is a map of the stone's inclusions, drawn with symbols. The proportions diagram shows angles and percentages such as table and depth. Together they act like a fingerprint for the diamond.
7. Comments
Any additional notes, such as clarity characteristics not shown on the plot. Always read this line.
How to verify a GIA report
Ask the seller for the report number.
Enter it in GIA's free Report Check on gia.edu.
Compare the online result with the paper report and the stone's measurements and inscription.
If the details do not match, do not buy.
Buying a certified diamond from Anjanee
At Anjanee Diamonds in Gems Tower, Bangkok, we share the report number for any certified stone so you can check it yourself before you decide. Looking for a particular shape, size or grade? Message us on WhatsApp at +66 81 583 1300 and we will help you find it.
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