Spread is a term used to describe how big a diamond is, and is usually measured by the diameter or length and width of a diamond.
However, it is important to realise that the diameter can sometimes be misleading, as a 0.5 carat round diamond will have a diameter of around 5.2mm, whilst a 1 carat round diamond will have a diameter of around 6.5mm.
Whilst 1.3mm in diameter may not seem like much, if you consider the total surface area of the diamond the one carat round diamond, then it works out to be about 56% bigger than the 0.5 carat round diamond.
That said, the spread of different shapes varies widely. For example, a 1 carat princess cut only has a length and width of around 5.5mm, simply because princess cuts are cut deeper than rounds.
Despite the importance of spread, most people still relate a diamond’s size to its carat weight. This could possibly be the worst thing that a diamond buyer could do, as cutters can use all sorts of “tricks” in order to cut a diamond with a bigger carat weight, such cutting a thicker girdle. On the other hand, it is important to realise that there is an ideal spread range for each carat weight.
Therefore, a very shallow diamond, and hence one with a bigger spread will not return the optimum amount of light.