Carat - A bigger diamond is not always a better diamond

The carat is the standard measure of the weight of a diamond. Many people choose a diamond based on how many carats it is, in the often mistaken belief that a larger stone is inherently more desirable and valuable than a smaller stone.

However, a large stone holds little value if it lacks brilliance, purity and high-grade colour. So when choosing a diamond, size alone is almost meaningless unless you also consider its cut, colour and clarity.

Although there is a relationship between weight and visible size, it is by no means fixed. For example, a poorly-cut 0.65ct diamond can have the same visible area, or diameter, as a well-cut 0.55ct diamond, as shown in the diagram below.

Once set into jewellery, the two stones will look the same size, but the heavier one will be dull and lifeless when compared with the lighter, less expensive and more brilliant stone.

Size does, however, increase the value of a well-proportioned stone of good colour and clarity, simply because large diamond naturally occur more rarely than small ones.

The diagram on the right illustrates the typical size of diamonds that are cut to ideal proportions.