CARAT WEIGHT: The standard unit of measure for diamonds and other gemstones is the carat. One carat is equal to 1/5 of a gram, or 1/142 of an ounce. The carat is also referred to as containing 100 "points". Therefore, a 50-point diamond weighs ½½ carat, a 25-point diamond weighs ¼¼ carat, and so on. The price per carat of diamonds can at times increase exponentially with size, due to the rarity of larger gemstones. A one-carat diamond typically costs 3.5 to 4 times what an equivalent ½½ carat costs, and the same goes for subsequent increases in size.