11" Gravitron® gravity water pipe with 12mm funnel bowl measures 3.5" in diameter.The medium Gravitron is 11" tall and 3.5" in diameter. The outer base is designed to hold 8" of water. As the inner bottle is pulled slowly upward, smoke from the 12mm bowl fills the chamber. Once the bowl is removed, the 16mm downstem doubles as a mouthpiece. Lowering the bottle back into the chamber forces smoke up through the downstem in a pressurized flow. The Gravitron is the first all-glass gravity smoking system and GRAV's namesake.