Detailed explanation of diamond quality classification

The most important and simplest of the 4Cs of diamond classification is quality classification. Usually it is based on direct weighing.

A. Diamond quality classification

1. Diamond mass unit
   
   1) Gram (g): It is the legal measurement unit in my country. When the mass of diamond is expressed in grams, it is required to be accurate to 0.0001g.
   
   2) Carat (ct): It is an internationally accepted gem mass unit.
   1ct=0.2g =200mg (1 carat = 0.2 grams = 200 milligrams) 1g=5ct (1 gram = 5 carats)
   
   When the mass of polished diamonds is expressed in carats, it is required to be accurate to two decimal places, and the third place is rounded up. For example, 0.598ct should be recorded as 0.59ct; and 0.599ct can be recorded as 0.60ct.
   
   3) Point (pt): It is an internationally accepted gem mass unit, mostly used for measuring diamonds below 1ct.
   1ct=100pt (1 carat = 100 points)
   
2. The approximate relationship between the diameter, height and quality of round diamonds
   
   The similarity of the cutting angle and method of round diamonds determines the relationship between their diameter, height and quality.

B. Diamond weight classification

Although “carat” is a very small unit, there are not many diamonds over 1 carat, and most finished diamonds are less than 1 carat.

1. According to the customary classification of the diamond industry, diamonds below 0.05ct are broken diamonds, 0.05ct-0.22ct are small diamonds, 0.23ct-1ct are medium diamonds, 1ct and above are large diamonds, 10.8ct-50ct are extra-large diamonds, and 50ct and above are named diamonds. Generally speaking, unless the color is rare or there are other special features, only giant diamonds weighing more than 100ct are qualified to be recorded in the history of world famous diamonds.
   
2. According to commercial grading, diamonds below 6 carats are divided into different weight ranges, which are more delicate. Each range is a level, and there are 18 levels in total:
   a) 0.01-0.03ct;
   b) 0.04-0.07ct;
   c)0.08-0.14ct;
   d)0.15-0.17ct;
   e)0.18-0.22ct;
   f)0.23-0.29ct;
   g)0.30-0.37ct;
   h)0.38-0.45ct;
   I)0.46-0.49ct;
   j)0.50-0.69ct;
   k)0.70-0.89ct;
   l)0.90-0.99ct;
   m)1.00-1.49ct;
   n)1.50-1.99ct;
   o)2.00-2.99ct;
   p)3.00-3.99ct;
   q)4.00-4.99ct;
   r)5.00-5.99ct;