Pearl sizing varies widely depending on the type of pearl that is being evaluated. Generally, the smallest pearls are available in Akoya cultured pearls, where you can find natural cultured pearls as small as 4.0 millimeters in diameter. Akoya pearls usually have a maximum size range of approximately 9.5 to 10.0 millimeters in size.
While Akoya pearls have the smallest range of sizes, freshwater pearls usually fall in the mid-size range with pearls ranging from 6.0 millimeters to approximately 12.0 millimeters. Freshwater pearls larger than 12.0 millimeters are extremely rare and hard to find.
The largest pearl sizing is available through south sea pearls, where the largest and highest quality pearls are available. South sea pearls include numerous types of pearls including Black Tahitian South Sea Pearls, Golden South Sea Pearls, and White Australian South Sea Pearls. South Sea pearls usually start at approximately 8.0 millimeters in diameter and have a maximum range of 16.0 millimeters at times. South Sea pearls with sizes of 14.0mm and above are extremely rare, and high quality pearls in that size range can costs thousands per pearl.