While these tanks technically have the capacity to hold 20 lbs most all propane tanks are only filled to 80% capacity with LP (liquid propane)that equals 16 lbs for a 20 lb tank the other 20% is gas. In many states it's the law because of safety concerns.
Here's a piece that explains it a little better:
http://arfarfarf.com/fire/articles/propane_weight.php
They do the same thing with large stationary tanks that are built with steel 1/4 in. thick. The propane company will only put 400 gal in my 500 gal tank. So you really don't want those thin portable tanks filled to capacity. Some guys haul these things around inside their cars! At extremely high temp a completely filled LP tank would be very dangerous.
LP weights 4.2 lbs per gal at 60*F so you get slightly less than 4 gal per 20 lb tank. So if Blue Rhino is shorting you 1 lb that's only about 1/4 gal or $1 worth at $4/gal.
Not defending Blue Rhino here their prices are outrageous I just wanted to shed some light on a commonly misunderstood topic.
But remember you are paying a premium for convenience. And you really can't blame them for wanting exclusive rights if they can get it. It's up to the consumer to put a stop to that practice by buying elsewhere. I would agree that it's underhanded not to inform a customer that the tank could not be filled elsewhere if that's their practice. It's also bad business practice people will eventually catch on and the smart ones will take their business elsewhere. But many people won't and they say nobody ever lost any money by underestimating the intelligence of the american consumer.
