How big is a 4 carat sapphire?

A 4 carat sapphire typically measures about 10 to 11 millimeters in diameter, depending on its cut. Carat weight refers to the gemstone's weight rather than its dimensions, so two sapphires of the same carat weight can vary in size based on their shape and cut. Generally, a well-cut sapphire will have a balanced appearance and good brilliance.