Gallstones or Gallbladder Stones are the hardened pebble-like particles that form in the gallbladder. The sizes of these gall bladder stones or gallstones can span from a few millimetres (as a grain of sand) to as large as 4.3 cm (as large as a golf ball). There could be a single massive gallstone, hundreds of smaller stones, or a combination of small and large stones in the gallbladder. In medical term, it is called cholelithiasis.