Messuring propane how many gallons equals 20lbs?

4.7 gallons = 20 pounds of propane.

https://www.askmehelpdesk.com/plumbing/advice-plumber-796884.html

Are you trying to change from natural gas to propane?

I sincerely hope you are not attempting to convert the hot water heater you mentioned in your first post to run on propane. If you are in an apartment, this is no doubt against your lease, extremely dangerous and, if you have the tank inside the building, illegal in most if not all states. What are you planning? Don't know your exact plans but if you are considering LPG conversion under these circumstances, we will not help you do something of this nature. You never responded to questions from your previous post regarding an electric install.

No I'm going to put the gas on in my daughters .name I cantvput my kids life in danger but if you go on line the triton camp chef or the eco portable shower are legal and can be used indoors and are very safe for apartments thank you

Oh and the marey potrable shower to are safe and that will be my alternitive if I can't put the gas on

From Triton Q&A web site--
"The unit vents heat out of the top of it. In order to install it in a cabin(indoors) I would think you would need to vent it to the outside somehow. I would probably mount it on the outside of the cabin and run the water lines through the wall". Not safe vented indoors and a propane bottle of that size indoors is most likely illegal.

I'm 42yrs old and very intelligent I went to collage I have been researching this for awhile now and these units don't need vents and I have a window and vent in my bathrom

Im going to buy the indoor unit at walmart for $115,00 just in case just to have and now I'm going to research if its illegal to have propane indoors in mass. Thank you for letting me know that info because I didn't no that

I do not wish to criticize but don't want you to have an accident that may hurt you or others living in your apartment or apartment building. Tanks of propane inside are extremely dangerous.