(From the Four Cs) Carat Weight is the WEIGHT of the diamond. This is often confused with size. "Size" is really Carat Weight. If an item has multiple diamonds, "ct. tw." will express the Carat Total Weight of all the diamonds in the piece. The graphic below shows the difference between diamond carat weights. Notice that a 2.00ct stone does not appear twice as large as a 1.00ct stone. Again, carat is not size, but weight. Thus, a 2.00ct stone does weigh twice as much as a 1.00ct.