Weight estimation formula for round Diamonds

Once the Average Girdle Diameter and the Depth are discovered it is possible estimate the weight of a Diamond just by applying a simple formula.
The formula is as follows;
Average Girdle Diameter x Average Girdle Diameter x Depth x 0.0061
So a Diamond with a Average Girdle Diameter of 6.5mm and Depth of 4mm will wight:
6.5 x 6.5 x 4 x 0.0061 = 1.03ct
It is important to know that the formula works only for Diamonds with good proportions, in some cases some modifications have to be made, so never rely only on the formula (non of the changes is extremely big, however if the estimated weight is 1.00ct it is possible that the Diamonds real wight is 0.94ct which have a lower per-carat price).