Diamonds are weighed on a scale of metric carats, abbreviated "ct." It is equal to approximately 1/5 of a gram. A carat is broken down into 100 points, just like a dollar is broken down into 100 pennies. When you see a diamond weight of 1.45ct, it means one carat and 45 points. The larger a diamond is the more rare it is. Diamonds are bought and sold on a pricing concept known as "per carat." As diamonds get larger, the price per carat increases due to the rarity factor, so a diamond that weighs 2ct. will be worth more than twice as much as a 1ct. diamond.