The unit of measurement used to measuring the weight of diamonds is carat (cts). One carat equals to 0.2 grams (about 1/142 oz) and is equivalent to 100 points. Half a carat is thus named 50 points. If other factors are equal, the more a stone weighs, the more valuable it is. Large diamonds are rarer than small ones; its value per carat increases as its weight increases.
The weight of a 1-carat diamond is equivalent to the added weight of four 0.25-carat diamonds; however, the 1-carat would cost much more than the sum of the four 0.25-carat diamonds. Some have misconceptions that a 3 carats diamond would be twice as big as a 1.50 carats diamond. A 3 carats diamond is only twice as heavy but not twice as big due to varying dimensions.