By The Eye desk · Last verified 28 September 2026
A diamond’s quality is described by the 4Cs, a system created by the Gemological Institute of America (GIA). Carat is weight, and one carat is 200 milligrams. Colour runs from D (colourless) to Z (light yellow or brown). Clarity runs from Flawless to Included. Cut, for round diamonds, is graded from Excellent to Poor. A grading report records all four, plus measurements, polish, symmetry and fluorescence, and a report number laser-inscribed on the stone lets you check that the paper matches the diamond.
Quick facts
- Carat is weight, not size: 1 carat = 200mg.
- Colour: D (colourless) to Z (light yellow or brown).
- Clarity: FL, IF, VVS1–2, VS1–2, SI1–2, I1–3.
- Cut (round brilliants): Excellent, Very Good, Good, Fair, Poor.
- Report numbers are laser-inscribed and can be checked online.
- GIA inscribes lab-grown stones “LABORATORY-GROWN”.
What do the 4Cs mean?
| C | What it measures | Scale |
|---|---|---|
| Carat | Weight | Recorded to a hundredth of a carat |
| Colour | Absence of colour | D (colourless) to Z (light yellow or brown) |
| Clarity | Inclusions and blemishes, seen at 10× magnification | Flawless (FL), Internally Flawless (IF), VVS1–2, VS1–2, SI1–2, I1–3 |
| Cut | How well the stone returns light: proportions, polish, symmetry | Excellent to Poor (round brilliants) |
The Cs work together. A well-cut diamond can look larger than a poorly cut one that weighs more. For most people, the difference between D, E and F colour is barely visible to the naked eye.
What does a grading report show?
A GIA Diamond Grading Report records the 4Cs, a plotted diagram of where the inclusions are, the measurements and proportions, the polish and symmetry grades, and fluorescence. It also notes any treatments detected. GIA’s shorter Diamond Dossier omits the clarity plot but carries the same grades.
How do I check the report is real?
Graded stones carry a laser-inscribed report number on the girdle, the thin edge of the diamond. A jeweller can show it to you under magnification, and you can check it against GIA’s online report database.
What about lab-grown diamonds?
They’re graded on the same colour and clarity scales, but GIA’s reports for them are separate documents. Every lab-grown stone GIA grades is laser-inscribed “LABORATORY-GROWN” with its report number. The grades describe quality; they don’t mean the same rarity as the equivalent grade in a natural diamond.
The WahLiao Verdict
Buy the report as well as the stone: ask for it, read it, and check the inscription against it. Spend on cut first, because that’s what makes a diamond sparkle, and save on the colour and clarity grades you can’t see.
Questions people ask
Is a bigger carat always better?
Not necessarily. Cut affects how big and bright a diamond looks.
What does “eye-clean” mean?
That no inclusions are visible without magnification, even if the clarity grade isn’t top.
Is fluorescence bad?
It’s a stone’s glow under ultraviolet light; the report notes its strength so you can judge it in person.
Are other labs’ reports the same?
Other labs use similar scales, but grading standards can differ. Compare like with like.
Sources: GIA, laboratory-grown diamond services; Centurion on GIA lab-grown reports; Jewellery News Asia on lab-grown report types; Skyjems, GIA grading report reference; Rêve Diamonds on reading a GIA report.
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