A carat is the unit of measurement that is used to measure the weight of a diamond. The heavier a diamond is, the rarer, and in turn, the more expensive it is. There are fewer than one million mined rough stones in the world that are large enough to yield a 1 carat diamond. This goes to show how truly rare a 1 carat diamond actually is.
A metric carat is equal to 200 milligrams, and each carat is subdivided into 100 “points.” For example, a one carat diamond is equal to 100 points and a .5 carat diamond is equal to 50 points. The carat weight of a diamond is written in decimal numbers (e.g. .70 carats) but it is usually expressed in fractions. For example, a diamond that is between .70 and .83 carats is often expressed as 3/4th of a carat.
While grading the other four C’s can be slightly subjective, carat weight is generally the most objective of a diamonds quality.