[DadsHemi]

It seams to vary who fills the tanks, I can tell you a 30lb bottle will hold 7.2 gals of propane but will be over filled and trip the overfill safety, I believe typically 6.8 gals is on an empty bottle when completely empty would be the norm. A few weeks ago here in Fort Smith AR it was 21 degrees in the early nights to early mornings and had a bottle run out, it switched over so I took the empty bottle to tractor supply and all that went into it was 5.6 gals. When the temps go very low the propane won’t boil off enough vapor gas to build enough pressure and thus that’s why the auto regulator will switch over bit yet propane it left in the other bottle. If your not using the or have an auto regulator it’s going to act empty.