Carat refers to a diamond's weight and gives you a sense of its size. The unit of weight for diamonds is the metric carat, which is one-fifth of a gram and is divided into 100 points. A bigger diamond doesn't always mean a more expensive one; you have to consider all the 4 C's.
Here's a tip: When you compare diamond carat sizes, consider a diamond's cut. A high-carat diamond with a poor cut grade can look smaller, often featuring a deeper cut, rather than a diamond with a smaller carat and a far better cut.