The diamond guide
Read a diamond the way a gemologist does.
A certified diamond comes with a grading report: an independent description of one stone. Here is what each line on it means.
The report
What a GIA report records
GIA, the Gemological Institute of America, examines a stone and records what it finds. The report belongs to that one stone, and its number is the stone's identity.
- 01Report number and date
- 02Shape and cutting style
- 03Measurements in millimetres
- 04Carat weight
- 05Colour grade
- 06Clarity grade
- 07Cut grade, for round brilliants
- 08Polish and symmetry
- 09Fluorescence
- 10A plot of the inclusions and a proportions diagram, on the full report
- 11The inscription on the girdle
Colour
From D to Z: how little colour a diamond has
Colour is graded by its absence. D is the top of the scale, with no colour a trained eye can see; each letter down the alphabet carries a little more warmth, up to Z.
- D
- E
- F
- G
- H
- I
- J
- K
- L
- M
- N
- O
- P
- Q
- R
- S
- T
- U
- V
- W
- X
- Y
- Z
Clarity
From flawless to included
Nearly every diamond carries tiny marks of its making: crystals, feathers, clouds. Clarity grades how many there are, how large and how visible, seen under ten times magnification.
- FL
- IF
- VVS1
- VVS2
- VS1
- VS2
- SI1
- SI2
- I1
- I2
- I3
- FL
- Flawless
- IF
- Internally flawless
- VVS
- Very, very slightly included
- VS
- Very slightly included
- SI
- Slightly included
- I
- Included
Cut
Cut decides how it returns the light
A well cut stone sends the light that enters it back up through the top. Too shallow or too deep, and light escapes through the bottom. GIA grades the cut of round brilliants in five steps.
- Excellent
- Very good
- Good
- Fair
- Poor
Carat
Carat is weight, not size
One carat is 0.2 grams. Weight grows with volume, so a stone of twice the weight is only about a quarter wider. The circles show round brilliants of the same proportions, drawn to their relative diameters.
- 0.5 ct
- 1 ct
- 2 ct
- 3 ct
- 5 ct
1 carat = 0.2 g
Fluorescence
A glow under ultraviolet light
Some diamonds glow under ultraviolet light, most often blue. The report records how strongly. It describes the stone; it is not a grade of quality.
- None
- Faint
- Medium
- Strong
- Very strong
The inscription
A number written on the stone itself
Most certified stones carry a unique number laser inscribed on the girdle, the thin edge around the widest point. It is too small to see without a loupe, and it matches the number on the report.
You can check any GIA report on GIA's own site: gia.edu/report-check-landing