you forgot to mention the weight of the hose.

I backfill all of my tanks from a 100 pound cylinder flipped upside down on a cherry picker... i've accidentally filled tanks to at least close to 100% capacity and all it does is in warmer temperatures is bleeds off the excess Through the over pressure valve that all cylinders have.... when this happens I will bleed the cylinder off into another tank until I reach the proper weight as described in this video..

Here in Texas, the local propane truck meters are set one a year and calibrated for 60 degree days. The day my two new tanks were filled it was 37 degrees the night before and maybe got to 46 that day. Both tanks were "Dosed" with 8 gallons of Propane before being moved into their fixed placement. When the truck that has the FIXED temp. calibration meter pumped both tanks , on each tank 75% full registered on each gauge, the truck meter said I got 400 gallons in each tank. Safely, how many gallons did I actually get?

In Canadian Tire in Oshawa on Gibb will only fill 3 lb to 5 lb propane tank thy say its a low

should the 80% be 16 lbs. instead of 20 lbs.?