A 20 pound LPG tank does not weigh 20 pounds. It actually weighs 18 pounds when empty, which is known as the tare weight.
When filled with gas it weighs 38 pounds, hence the name referring to the weight of the gas. Another weight listing is WCW which means water capacity weight, or the weight of the tank if filled with water.
For a 20 pound tank that weight would be 48 pounds.
A 20 pound tank measures 18 inches high. In order to function, the LPG tank must remain upright so the height is important for space considerations as the tank cannot be placed on its side when being used for outdoor grills, its main use.
The tank has a diameter of 125 inches. The tank's interior capacity totals 47 gallons.
Length of Use
This specification refers to the length of time the tank can be used until it runs out of gas. The first factor in the determination of that time, measured by the British Thermal Unit (BTU), a unit of measurement for energy and heat output, is the BTU capacity of the tank, which for a 20-pound container is 430,270.
The second factor refers to the rate at which the appliance burns BTUs. An example would be a gas grill operating at capacity burning 40,000 BTUs an hour.
Such a grill would then expend all of the gas in just under 11 hours, assuming operation at capacity.