Cut, colour, clarity and carat: the four words that decide what a diamond is worth.
By Shreya S · Last reviewed 15 November 2026
What are the 4Cs?
A grading system popularised by the Gemological Institute of America (GIA) in the 1950s so that diamonds could be described the same way anywhere in the world. Cut is how well the stone has been shaped and polished, colour is how close it is to colourless, clarity is how free it is of inclusions, and carat is its weight. One carat is 0.2 grams.
How do the colour and clarity scales work?
Colour runs from D (completely colourless) to Z (noticeably yellow or brown); most people cannot tell neighbouring grades apart. Clarity runs from Flawless and Internally Flawless through VVS (very, very slightly included), VS and SI down to I (included). Many inclusions in VS and SI stones are invisible without magnification.
Which C matters most?
Most jewellers say cut, because it controls the sparkle. A well-cut stone returns light to the eye; a poorly cut one looks glassy or dark, whatever its colour and clarity. The classic round brilliant has 57 or 58 facets, and its proportions were mapped by Marcel Tolkowsky in 1919. Fancy shapes such as oval, emerald, pear and cushion are cut to different rules.
What does a certificate tell you?
An independent lab report, from the GIA or other labs such as IGI, records the stone’s 4Cs, measurements, fluorescence and a map of its inclusions, and says whether it is natural or lab-grown. Many stones carry a laser-inscribed report number on the girdle. Price jumps sharply at round weights such as one carat, so a 0.95-carat stone can look almost the same for much less.
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