The weight of a diamond is measured in carats. One carat is divided into 100 points, so that a diamond of 25 points is described as a quarter of a carat or 0.25 carats. The larger the diamond (and therefore the rarer) the more expensive per carat it will be. For example, a 1ct diamond costs much more than two 1/2ct diamonds and one 30 point diamond costs much more than 30 one point diamonds.
The Carat measurement of a diamond is actually a measurement of the Diamond’s weight rather than its size or diameter. Half carat diamonds while half the weight of a 1ct diamond, are not half the size. This is important to remember, as depending upon the proportions of the cut of the diamond, a diamond that weighs more doesn’t always look bigger. It is always better to have a smaller better cut diamond than one that purely weighs more. They will have the same diameter, but the smaller diamond will sparkle more. This is the reason why carat weight is the last thing that you should choose.