Classification of Diamond by Size

Diamond is valued on the basis of its carat weight, and not on its size. Size (diameter in mm) of diamond is used just for estimating its carat weight. However, sometimes size of diamond is also used as its identification.

Classification of Diamond according to Size

Diamonds of different sizes (irrespective of their other properties) are classified into different groups. Melee group or Star group comprises of diamonds of sizes ranging from 0.001 ct to 0.18ct. Stones between 0.12ct and 0.18ct are called Coarse Melee.

Dealers routinely use sieves (sieve set comprises of circular plates, each punched with precisely sized holes) to sort same sized diamonds.

Diamond Sieve Set

Tools used for Measuring Size of Diamond

Calipers and Leveridge Gauge are used to measure diamonds in mm size. Leveridge Gauge is used to measure diamonds, pearls and gemstones whether loose or mounted.

Since round brilliant cut diamonds have exact standards, you can estimate the carat weight of diamond based on its diameter.

The following picture shows the mm size and the corresponding carat weight of round brilliant cut diamond. Please note that it is not applicable for other type of cuts and shapes of diamond and also is not applicable for gemstones.

As shown above, 1 carat round brilliant cut measures approximately 6.5mm. On the other hand, princess cut of same weight (i.e. 1 carat) measures 5.5mm (always remember that princess cut diamond is heavier than round brilliant cut for the same size).

Above chart is for educational purpose only, and it should not be used as the basis for mapping size and weight of diamond. It is only when you deal regularly in diamonds, the mm sizes can be remembered.

It should be noted that the size of the diamond is also referred as the Spread of the diamond.

Often diamonds are cut “heavy” i.e. minimum cutting is done to avoid weight loss. In such a case, diamond will have large diameter but smaller depth. However, if it is cut too deep to have better cut, it may have smaller diameter and this diamond will appear comparatively smaller when viewed from top.

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