Carat weight is the simplest part of the Four Cs. Diamonds are weighed on a decimal scale. A diamond that weighs .10 is a 1/10th-carat diamond. A diamond that weighs 1.25 carats is a 1¼-carat diamond. Pricing is where diamond weight comes into play. There are some natural price breaks that are directly related to weight. As an example, from .69 to .70 there is about a 20 percent price increase between the same qualities.