So, what you are probably re â¦ ferring to is 'energy'. The SI unit of energy is the joule (J). An alternative unit, used by electricity utility companies for the purpose of billing its consumers, is the kilowatt hour (kW.h).
a typical steel 30 pound liquid propane tank weighs about 25-28 pounds empty. propane tank markings (on collar) propane weighs about 4.125 pounds per gallon and a 30 po â¦ und tank will hold about 7.5 gallons so a full tank will weigh about 55 pounds or so. /source: wiki.answers.com/.
Therefore, a 20# cylinder filled to maximum safe capacity will contain (20# / 4.24gal/#) = 4.7 gallons of propane. If you take a propane tank to a service station and fill it all the way, you will leave with 4.7 gallons in your tank, because they will not fill the tank beyond its maximum safe capacity.