How to check if there is still gas left in a propane tank?

Question

How to check if there is still gas left in a propane tank?

Answer 1

Tap the side of the bottle with something and then swirl the bottle. If you hear the pitch changing there is liquid inside. BTW there may still be gas even if no liquid is present.

Answer 2

pick it up to see how heavy it is

Answer 3

Weigh it.  The cylinder itself has its weight stamped on it somewhere.

DO NOT put an open flame near the outlet line.