Carat Weight

The carat (ct) is divided into 100 points — so a 0.50 ct stone is a 'fifty-pointer.' The term derives from the carob seed (Ceratonia siliqua), historically used as a balance weight because of its purportedly consistent mass, though modern standardization has nothing to do with actual seeds. The metric carat was standardized internationally in 1907. Price-per-carat increases non-linearly with size for fine gems — a 3 ct ruby of equal quality does not cost three times as much as a 1 ct stone, but often ten to thirty times more, because larger fine stones are exponentially rarer.