Reading a GIA certificate
The GIA (Gemological Institute of America) is a non-profit institute and the creator of the 4Cs system: colour, clarity, cut and carat. Here are the 15 areas of a report, in the order they appear.
Illustrative layout of a GIA report. This is not a real certificate.
- 1Report date and number
The number is unique and recorded in the GIA database. It lets you check the report online. Verify my GIA certificate
- 2Shape and cutting style
The outline of the stone and the arrangement of its facets, for example "Round Brilliant".
- 3Measurements
For a round stone: minimum and maximum diameter, then depth, in millimetres (for example 6.41 to 6.43 x 3.97 mm).
- 4Carat weight
The weight of the stone. Two diamonds of the same weight do not necessarily look the same size: see the measurements.
- 5Colour
From D (colourless) to Z, compared against GIA master stones. A star (*) means a colour treatment was detected.
- 6Clarity
From FL (Flawless) to I3, observed under 10x magnification according to the size, nature, number, position and relief of the inclusions.
- 7Cut grade
From Excellent to Poor. This overall grade exists only for round brilliant diamonds in colours D to Z.
- 8Polish and symmetry
Two separate grades, from Excellent to Poor: how smooth the surface is and how precise the facets are.
- 9Fluorescence
How the stone reacts to ultraviolet light. "None" covers a range from undetectable to very faint.
- 10Inscription
The report number, sometimes a word, laser-inscribed on the girdle. It links the stone to its certificate.
- 11Comments
Additional information, for example a detected treatment such as laser drilling.
- 12Proportions diagram
The profile of the stone with its real proportions: table, depth, angles.
- 13Clarity plot
A drawing of the stone where symbols locate each inclusion. The key to the symbols comes with it.
- 14GIA scales
The colour, clarity and cut bars showing where your stone sits.
- 15Security and QR code
Microprint, hologram, watermark and QR code that let you check the report in the GIA database. Verify my certificate
Reading an HRD Antwerp certificate
HRD Antwerp is the laboratory of the Antwerp Diamond High Council, in the world capital of diamonds. An HRD report holds the same main information as a GIA report, with a few differences in vocabulary worth knowing.
| On an HRD report | What it means |
|---|---|
| Colour | A scale from D to Z, with names: D "Exceptional White+", E "Exceptional White", F "Rare White+", G "Rare White", H "White", then the more noticeable tints. |
| Clarity | The top grade is called LC ("Loupe Clean"), followed by VVS1, VVS2, VS1, VS2, SI1, SI2 and the P1 to P3 grades. |
| Cut | Three separate grades: proportions, polish and symmetry, each rated Excellent, Very Good, Good or Fair. |
| Fluorescence | A scale from nil, slight and medium to strong, measured under long-wave ultraviolet light. |
| Verification | Enter the report number on the laboratory's website; digital reports also carry security codes. Verify my HRD certificate |
You can check a report online from my page Verify a certificate.
GIA and HRD, side by side
Both laboratories are serious and independent. Their scales look alike, but their grades are not officially equivalent: always compare the measurements and proportions, not just the words.
| GIA | HRD Antwerp | |
|---|---|---|
| Colour | Letters D to Z | Letters D to Z, with names (Exceptional White+...) |
| Highest clarity | FL (Flawless) | LC (Loupe Clean) |
| Lowest clarity | I1, I2, I3 | P1, P2, P3 |
| Cut | One overall grade for the round brilliant, Excellent to Poor | Three grades: proportions, polish, symmetry |
| Fluorescence | None, Faint, Medium, Strong, Very Strong | Nil, slight, medium, strong |
Other laboratories
Other laboratories, such as IGI, also issue reports. Each has its own grading method. Whatever the laboratory, here is what to check before you buy.
- The report number matches the stone (ideally laser-inscribed on the girdle).
- The report can be checked online, with the number or the QR code.
- The weight and measurements match what is advertised.
- Colour and clarity are read on the laboratory's own scale, not on another one's.
- The report states "natural" or "laboratory-grown" without ambiguity.
- Cut, polish and symmetry are given. For fancy shapes there is generally no overall cut grade.
- Fluorescence is mentioned.
- The comments report no treatment.
- Above all: the stone has been seen, on video or in person. A report describes a diamond, it does not replace your own eyes.
The ideal measurements
For a round brilliant diamond, the GIA gives these proportion ranges for the Excellent cut grade. It is a guide, because the final grade depends on all the proportions together and not on a single figure.
| Proportion | Range for Excellent |
|---|---|
| Table | 52 to 62% |
| Crown angle | 31.5° to 36.5° |
| Pavilion angle | 40.6° to 41.8° |
| Star length | 40 to 70% |
| Lower girdle length | 65 to 90% |
| Culet | None, very small or small |
Source: GIA 4Cs, "Diamond Anatomy".
| Weight | Indicative diameter |
|---|---|
| 0.30 ct | 4.27 to 4.37 mm |
| 0.50 ct | 5.07 to 5.18 mm |
| 0.75 ct | 5.80 to 5.93 mm |
| 0.90 ct | 6.16 to 6.30 mm |
| 1.00 ct | 6.38 to 6.53 mm |
| 1.50 ct | 7.31 to 7.47 mm |
| 2.00 ct | 8.04 to 8.22 mm |
Estimate for a round brilliant with a total depth between 59 and 63%. This is my own indicative calculation, not provided by the GIA.
What does 3EX mean?
3EX means "triple Excellent": cut, polish and symmetry all receive the top grade. For a round brilliant, it is the most demanding level a GIA certificate can give.
Find my diamondFrequently asked questions
What does 3EX mean on a diamond certificate?
3EX means "triple Excellent": the cut (proportions), the polish and the symmetry each receive the best grade, Excellent. This cut grade exists only for round brilliant diamonds.
What is the difference between a GIA and an HRD certificate?
Both are serious, independent laboratories. Their scales look alike but their words differ: HRD names the colours (Exceptional White+, Rare White...) and grades the cut in three separate grades, while the GIA uses the letters D to Z and gives one overall cut grade for the round brilliant. The grades are not officially equivalent.
Is a certificate enough to choose a diamond?
No. The certificate describes the stone precisely, but two diamonds of the same grade can look less alike than you would expect. That is why I send videos of the stone: the report is a tool, not a verdict.
How can I check that a certificate is genuine?
Each report carries a unique number, often laser-inscribed on the edge of the diamond (the girdle). You enter it on the laboratory's website, or scan the QR code, to compare weight, colour, clarity and measurements.