[TowerTalk] Bag concrete question

[r miles]

I just purchased a used HyTower & I'm getting ready to dig the hole. 
I've poured a bit the concrete before. Either redi-mix or small bag 
jobs. I have looked  several places at the 60 lb. homeowner type bags. 
Those are OK  but my question is cubic volume. None of the 60 lb. bags 
show cubic volume. I'm guessing it's 1 cubic foot of concrete in one of 
those. Anyone know what the cubic value is?
K9IL