By using Ultrasonogram the smallest size of gallstone which can be confidently diagnosed is of size:
Ultrasonography of the gallbladder is very accurate in the identification of cholelithiasis. Stones as small as 1.5 mm in diameter may be confidently identified provided that firm criteria are used. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Page 2619
1.5 mm
3 mm
5mm
10 mm