What does carat mean in diamonds?

A 'carat' is a unit of measurement used in the diamond industry to specify the weight of a diamond. A carat is equal to 200 milligrams, so a 5-carat stone weighs 1 gram.

​Is diamond carat the same as size?

No - people often assume a diamond's size is synonymous with its carat weight, but this isn’t always the case. There are other factors that can affect the size of a diamond.  Visually, different diamond shapes can make diamonds of the same carat size appear larger or smaller. For example, a marquise diamond will always appear larger than an oval diamond, simply because it has a larger surface area.  Similarly, the cut of a diamond can also impact the size of a diamond. Poorly cut diamonds that change in depth or feature a thick girdle often weigh more but appear smaller because their weight sits in the base of the diamond. In turn, there is less surface area on top - so not only does your diamond appear smaller, it will also sparkle less.