Carat is the unit that measures a diamond’s weight, not its face-up size. A 1.0 carat round diamond typically measures about 6.5 mm across, while a 2.0 carat diamond is about 8.2 mm. As carat weight increases, the diameter grows gradually but the overall depth increases faster, which can make two stones with the same weight appear different in size.

Diamond shape also changes how large it looks on the hand. Ovals and elongated cuts appear bigger than round diamonds of the same carat weight, while deeper cuts like cushions look smaller. Most engagement rings feature center stones between 1.0 and 3.0 carats, balancing presence, comfort, and budget.

When choosing, focus on millimeter size rather than carat weight alone. The right proportions create the best visual impact for your finger size and ring style.