Propane tank gets 4.23 - 4.70 gallons -so safe to say they fill it with 4 gallons + or - some.some company`s are charging same rates but giving you less fuel.they fill it on a scale.they just move the scale and give you less.
How Many Gallons Of Propane Does A 20 Lb Propane Tank Hold?
8 gallons. Companies charge by the cylinder size so it doesn't matter how many gallons are actually in the cylinder or not. It's a set price whether you have a 10#, 20#, 30# etc.