Carat is a term used to express the overall weight of a diamond, not its size as many people mistakenly believe. Each carat is subdivided into 100 'points' which allows for very precise measurements of diamonds and gems to the hundredth decimal place.
A diamond that is less than one carat in weight will be referred to by its points alone. For example, a diamond that weighs 0.75 carats would be referred to as a 'seventy-five pointer'.
Now as we mentioned, carat refers to the weight, not the size of the diamond and you may find that some diamonds of the same carat weight can look larger or smaller because of variations in shape and cut.
For example, a pear shaped diamond may be longer and thinner than another that is shorter or thicker.