Carats refers to weight, not size. You should ask for measurements. Two round diamonds of equal carat weight are not necessarily the same size. Also the shape is a factor. A 1.80 ct pear shape...
"18K" should be stamped on the inside of a ring band or near the clasp of a bracelet or necklace if it is 18 karat gold. No stamp may mean it is custume jewelry or the stamp may be worn off. A...