The full weight of a 30-pound propane tank is approximately 55 pounds, when the tank is completely filled. The size of a propane tank that holds 30 pounds of propane is a 7-gallon bottle.
A 7-gallon bottle of propane is often used for occasions such as RV travel, grilling and camping. This size propane bottle or tank holds roughly 640,500 BTU when filled to capacity. A 10-gallon bottle of propane holds roughly 40 pounds of propane and weighs 70 pounds when full. A small bottle of propane, such as a 5-gallon bottle, holds 20 pounds of propane and weighs 40 pounds when full. Propane bottles and tanks are always filled by weight.