The weight of a diamond is always given in carats and the international abbreviation, ct is used. The weight is indicated in certificates with 2 decimal places. Measurement is done with an accuracy of 3 decimal places. The second decimal place can only be rounded up if the third decimal place is 9.
1 ct = 200 mg = 0.2g
According to the strict defined parameters of a brilliant cut, it is possible to count the weight also by measuring the basic proportions of a brilliant-cut diamond, e.g. with the diameter (at least two axes perpendicular to each other) and height. Estimated density [ct] = (girdle circumference) 2 × height × 0,0061. The carat unit comes from middle age marketplaces where carob seeds were used as a weight unit for trading with precious stones because of their reputation for having a uniform weight.