are so valuable, its essential to have a universal grading system for comparing their quality. That's why in the 1940's GIA developed the 4C's and the Internet Diamond Grading System to objectively compare and evaluate diamonds.
Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. (Dont confuse carat with karat, as in 18K gold, which refers to gold purity.) Just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four Cs: clarity, color and cut. The majority of diamonds used in fine jewelry weigh one carat or less.