The carat is a unit of mass and 1 carat equals to 200 mg same as a small paper clip, or 0.2 grams. Diamonds and other gemstones are weighed using metric carats as their weight. One carat is divided into 100 points so a 0.50ct diamond is 50 points. Two diamonds with the exact same carat weight can vary greatly in price because of variations in color cut and clarity.

Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. In the diamond industry weight is often measured to the hundred thousandths of a carat and rounded to a  hundredth of a carat.  Diamonds that weigh more than one carat are expressed with a decimal. (For instance, a 1.08ct. stone would be described as “one point oh eight carats” or “one oh eight”.

As the carat weight of a diamond increases so does its rarity and therefore its price. Larger rough gems of high quality are much harder to find than smaller rough gems of high quality, making them rarer and more valuable. As a result, carat weight affects price exponentially as it grows.  For example, a single two carat diamond will be more expensive than 2 individual one carat diamonds of the same quality.


It is important to bear in mind that diamond carat weight should not be confused with diamond size.  When you look at a diamond in its setting usually it is the top section of the diamond which is most visible and where the brilliance and fire shines out.  When measured from side to side we get diameter, most likely what we will perceive as the size.  This is not always directly correlated to the weight of the diamond.  The way in which the diamond is cut will greatly affect the diameter and brilliance of the diamond.

Diamonds with a poorer cut, for example a change of depth or a thick girdle, will maintain their heavy weight but “hidden” in the base of the diamond with less surface on top so they look smaller.  A poor cut also damages the diamond’s magnificent ability to reflect sparkling light which would make the diamond appear bigger.  A diamond with a lower carat weight but better cut grade may easily appear larger than a diamond with higher carat weight but poor cut.

Because of this, to understand true diamond size, one should account carat weight combined with two other features: 1) Cut quality 2) Diameter – the width of the top of the diamond measured in millimeters.

The approximate diameters of an ideal cut, round brilliant cut diamond are illustrated in the chart below: (Note a 2 carat diamond does not have double the diameter “look” of 1 carat)

Size is important of course to many people but we SRONGLY  advise against sacrificing the diamond cut in exchange for a larger stone.