The standard 20-pound propane tank holds about 4.7 gallons of propane. The average 20-pound tank weighs about 40 pounds and contains 430,000 BTU when full. People generally use this size propane tank for residential grilling, camping and cooking, and some residential gas grills come standard with 20-pound tanks.
Discovered in 1912, propane is related to natural gas and gasoline. It is a member of the liquefied petroleum family. Propane is a gas under normal temperature and atmospheric conditions and is a liquid when stored in tanks with moderate pressure. Propane takes up 270 times less space as a liquid than as a gas.