What size is a one carat tanzanite?

A one-carat tanzanite typically measures around 6.5 to 7.0 millimeters in diameter when cut into a round shape. However, the actual size can vary slightly depending on the cut and shape of the stone. Tanzanite's density is lower than that of diamonds, so a one-carat tanzanite may appear larger than a one-carat diamond of the same cut.