Diamond size and diamond carat guide

When buying a diamond engagement ring, the size of the diamond is often the first thing that comes to mind. As a precious symbol of your future together, it’s important that you are happy with your purchase, and have an understanding of how sizing works will offer valuable insights as you make your decision. The term ‘carat’ (commonly abbreviated to just ‘ct’) refers to the weight of a diamond, although it is often (incorrectly) used to describe the size of a diamond.

The definition of a carat has changed over time, but since 1913 the international standard has been 200 milligrams, or one-fifth of a gram.

Diamonds can range in weight from a fraction of a carat to several carats. Carats are divided into points where one carat equals 100 points, for example:

• ½ carat diamond – 50 point or 0.50 carat diamond
• ¼ carat diamond – 25 point or 0.25 carat diamond

Did you know

The word carat derives from the carob tree. Carob seeds, once believed to have a uniform weight, were used for centuries as the standard against which precious gems were weighed.

Given the rarity of large diamonds, their price will increase with caratage. You will find, therefore, that a single 2 carat diamond will cost significantly more than two 1 carat diamonds.

It is important to note that the appearance of a diamond does not grow in direct proportion to its carat weight. For example, the size of a 2 carat diamond will not be twice that of a 1 carat diamond.

When there is more than one diamond in an engagement ring, such as in a diamond pavé band or a three stone ring, the diamonds are weighed together, rather than individually, resulting in ‘total carat weight’.