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 1.07 ct. is referred to as "one carat and seven points."
With an accuracy of 1/100,000 carat, the IGI scales provide a highly precise diamond weight, down to the hundredth or thousandth of a carat.
It is important to note that diamonds of the same weight don't necessarily have the same size appearance. Those cut too shallow or deep may look small for their weight, or suffer in brilliance. As a reference, IGI recommends the following vertical spreads 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.