A stone's Carat is the weight of a stone and is referred to as Carat Weight. Originally derived from carob beans used on scales. Note that the specific gravity, density and composition of different stones will vary and thus calculations of size to weight ratio will differ from one stone to another. Not to be confused with the carat of precious metal.
A carat weight would be counted as one part of a hundred. So one carat is 100/100 parts and written as 1.00 carats. Often in the trade a person may refer to a weight as for example fifty points, this would be the same as half a carat and be written as 0.50ct. One carat weight is equivalent to a fifth of a gram, 1.00ct = 0.20g
The below carat weights are only a basic guide based upon the approximate carat weight of a diamond to each individual cut, accompanied with the recommended diameter measurements as seen from above. Measurements are only approximations, remember that a diamond carat is weight and not size and may differ from this guide and not to be used as an intensive reference.
 0.05ct = 2.5mm  0.50ct = 5.2mm  2.00ct = 8mm  0.10ct = 3mm  0.75ct = 5.9mm  3.00ct = 9.4mm  0.25ct = 4.1mm  1.00ct = 6.5mm  5.00ct = 11mm 

 0.25ct = 5mm x 3mm  1.00ct = 7.5 x 5.5mm  5.00ct = 12mm x 10mm  0.50ct = 6mm x 4mm  2.00ct = 9mm x 7mm   0.75ct = 7mm x 5mm  3.00ct = 10mmx 8mm  

 0.50ct = 6mm x 4mm  2.00ct = 10mm x 7mm  5.00ct = 15mm x 9mm  0.75ct = 7mm x 5mm  3.00ct = 12mm x 8mm   1.00ct = 8mm x 5mm   

 0.50ct = 8mm x 4mm  2.00ct = 12 x 6mm  5.00ct =  0.75ct = 9mm x 4.5mm  3.00ct = 14mm x 7mm  7.00ct = 18mm x 9mm  1.00ct = 10mm x 4.75mm  4.50ct = 16mm x 18mm  

 0.30ct = 4mm x 4mm  1.00ct = 6.5mm x 6.5mm  3.00ct = 9mm x 9mm  0,50ct = 5mm x 5mm  1.50ct = 7mm x 7mm  5.00ct = 11mm x 11mm  0,75ct = 6mm x 6mm  2.00ct = 8mm x 8mm  

 0.10ct = 2.5mm  0.50ct = 4.75mm  3.00ct = 9 x 9mm  0.20ct = 3.25mm  1.00ct = 5.5mm  4.00ct = 10 x 10mm  0.30ct = 4mm  2.00ct =  

 0.20ct = 4mm x 3mm  1.50ct = 8mm x 6mm  5.00ct = 12mm x 10mm  0.50ct = 6mm x 4mm  2,00ct = 8.5 x 6.5mm   1.00ct = 7mm x 5mm  3.00ct = 10mm x 8mm  

 0.10ct = 3mm x 2mm  0.30ct =5mm x 3mm  0.60ct = 6mm x 4mm  0.20ct = 5mm x 2mm  0.40ct = 6mm x 3mm   0.25ct = 5 x 2.5mm  0.50ct =  

 0.50ct = 4x4x4mm  2.00ct = 8x8x8mm  5.00ct = 12x12x12  0.75ct = 5x5x5mm  2.5ct = 9x9x9mm   1.00ct = 6x6x6mm  3.00ct = 10x10x10  

 