Carat is one of the 4C’s (color, cut, clarity and carat) used to describe a diamond stone. The term carat was borrowed from the Carob tree. The seeds of this tree are famous for their uniformity and consistent weight. Diamond and gemstones used to be weighed against carob seeds until a standardized weight was developed and one carat was fixed at 0.2 grams. One carat is also divided into 100 points such that a quarter carat is equivalent to 25 points.

The heavier the carat weight does not necessarily mean that the diamond carat sizes are equivalently larger though. This is because the size is distributed throughout the surface and depth of the stone. This also helps demystify why the size of 1 carat stone is not double that of a 0.5 carat stone.

Most if not all diamonds were formed billions of years ago. Further, they are found between 75 to 120 miles below the earth’s surface and it can take up to several thousands of years for them to rise up to a level where they can be mined. Accordingly, all diamonds are rare but the larger ones i.e. 1 carat and over are even scarcer. Essentially, larger diamonds have a greater weight per carat. This is also why diamond carat sizes have the biggest influence on the price of a diamond stone.

Many people are still not able to clarify the difference between diamond carat sizes and weights. In the diamond industry, size describes the actual measurements of the various dimensions of the stone, while weight describes the heaviness of the carat. The different proportions of a diamond will therefore generate stones of the same carat weight but which are different in size. This however is different from a situation where a diamond is "spread" to make it appear larger in the eyes of the consumer. It is therefore important that when considering buying diamond/s the consumers should clearly differentiate between weight and size in relationship to whatever diamond/s appeal to their tastes.

We mentioned earlier that the price of a diamond stone is determined by its carat weight. Understanding the mathematics behind the price of a diamond stone can help the customer end up with a good bargain for this normally expensive jewelry. Remembering that the greater the carat weight the rarer that stone will be, customers should expect to pay a premium for heavier carat stones and especially those greater than one carat.

When examining diamond carat sizes it is important to bear in mind that proportions play a very important role in the stone’s final appearance. The thickness of the edge (girdle) determines how large a diamond appears to be. The wider the girdle, the smaller the stone appears to be. This is so because the diameter of a diamond stone is widest at the girdle.