Carat

The weight or size of a diamond is measured in carats (ct.).

One carat weighs 1/5 of a gram and is divided into 100 points, so a diamond weighing 1.07carat is referred to as "one carat and seven points."

For Example 
0.75 carat = 75 points.
1/2 carat = 50 points.
1/4 carat = 25 points.

With an accuracy of 1/100 carat, the IGI scales provide a highly precise diamond weight, down to the hundredth of a carat.

As a reference, IGI recommends certain vertical spreads (see image) for round brilliant diamonds.

When diamonds are mined, large gems are discovered much less frequently than small ones, which make large diamonds much more valuable.

Diamond prices rise exponentially with carat weight. So, a 2-carat diamond of a given quality is always worth more than two 1-carat diamonds of the same quality.