Your traditional BBQ cylinder is more accurately described as a 20 lb. DOT cylinder and is designed to hold 20 lbs. of Liquid Propane Gas (LPG). However, most of the exchange cylinders you find in cages out front of retailers are filled to only 75% of capacity. While these cylinders are clearly marked 15 lbs., most of the general public does not know what propane weighs and how that translates into gallons. Propane weighs 4.1 lbs. per gallon, thus 15 lb. = 3.57 gallons or ¾ capacity. Our full cylinders mean less change outs and increased cooking time per cylinder!