Diamond weight is expressed in carats (ct.), which is a metric measurement equivalent to 0.2 grams. The carat weight of a diamond is usually expressed to 2 decimal places (e.g. 1.27 ct.). Some unscrupulous dealers may refer to a diamond as being 3/4 carats, when in reality it is 0.73 carats. This is why it is important to know the carat weight of a diamond in hundredths of a carat.

It is important to note that a 2-carat diamond will not appear twice as big as a 1-carat diamond when viewed from the top. Nor will a 2-carat diamond cost twice as much as a 1-carat diamond. Since larger diamonds are more rare, their prices increase exponentially with increasing size. Therefore, a 2-carat diamond will cost more than two 1-carat diamonds of the same quality.