Carat size is the simplest of the four “C’s” as a measure of a diamond’s quality.  However, it is not a direct measure of size (like inches or millimeters) but actually a measure of weight.  Each carat is equivalent to 200 milligrams, or about .007 ounces.  There are 100 points in a carat, so a “33 pointer” is equivalent to a third of a carat, or .33 carats. Diamonds of the same weight can differ on a basis of other factors, especially the cut, which influences size.  The correlation of size to value is an obvious one.  The larger a diamond is, the more valuable it is.