The weight difference between diamond ring 37c and 37ct: ct is carat unit, and C has no such unit name. Generally, there is no such thing as C. There is a conversion formula between CT and Pt: 1 carat (CT) = 0.2g = 100 minutes (PT). Ct is a carat unit. Although the abbreviation CT represents many words in different fields, in the field of jewelry, CT refers to the internationally used gem weight unit: carat, and the diamond weight unit less than 1 carat is expressed in minutes (Pt).