The weight of a diamond is measured in carats. One caret is divided into 100 parts called "points".

1 ct.=1.00 1/2 ct.=0.50

The value of two diamonds of the same weight can vary greatly depending on the color, clarity and especially the cut. Below are two identical pieces of rough, (uncut diamonds) each of the same quality and value. 

From one piece of rough a diamond has been cut to ideal proportions, retaining a weight of one carat. The light is totally reflected through the top.

This piece of rough has been "spread" in its cutting, resulting in a diamond weighing approximately 1.40 ct. NOTE: The girdle is thicker, the table is much larger, the angles are exaggerated, all at the expense of that diamond's ability to reflect light.