The carat weight is simply a measure of the weight of the diamond, this is not to be mistaken for it's size or spread. This is important to note, as diamonds of the same cut and carat weight can vary in size measurements. 

The price of diamonds increases as the carat weight goes up, however it is not the only thing to take into account when purchasing a diamond. Other factors which have a huge impact on the overall beauty of the diamond are its cut, colour and clarity. This is why it's important to take into account all of the 4C's of a diamond, not just it's carat weight.

One carat is equal to 200 milligrams and is divided into 100 points; this makes one point of a carat equal to 2 milligrams. This means that in the trade 1/2 a carat is referred to as 50 points. 

Seeing as the carat weight of a diamond does not necessarily indicate its size, it is important to take into account the diamonds cut grade as well as its carat weight.