Since they are used to adjust spring capacity for different loaded conditions, there is not a single pressure to which they should be inflated. Might be anywhere from 30-60 psi with some side to side difference for mine.
They should always have some pressure in them to prevent damage by pinching, and there is a maximum. For mine that would be 20 PSI and 105 PSI according to the instruction sheet; don't recall the manufacturer.
I measure ride height at rear bumper before I load, inflate the bags to bring it to that height after loading, and level side to side. What those numbers are would be meaningless to you, as you are not sitting in my gently sloping driveway.
