Number of Bags = Volume (in cubic yards) x Strength (in psi) / Bag Volume (in cubic feet)Formula: volume = πr^2h,number of bags = volume (in cubic yards) x strength (in psi) / bag volume (in cubic feet)Formula: volume = πr^2h, number of bags = volume (in cubic yards) x strength (in psi) / bag volume (in cubic feet)It is generally recommended to use rebar inside a Sonotube when filling it with concrete to create a foundation for a building or other structure. Rebar, or reinforced steel bar, is used to strengthen and reinforce concrete structures. When used inside a Sonotube, rebar helps to increase the tensile strength of the foundation and reduce the risk of cracks or other structural damage.Number of bags = volume (in cubic yards) x strength (in psi) / bag volume (in cubic feet)number of bags = volume (in cubic yards) x strength (in psi) / bag volume (in cubic feet)Formula: Volume = πr^2h, number of bags = volume (in cubic yards) x strength (in psi) / bag volume (in cubic feet)Formula: Volume = πr^2h, Number of bags = volume (in cubic yards) x strength (in psi) / bag volume (in cubic feet)Formula: Volume = πr^2h, number of bags = volume (in cubic yards) x strength (in psi) / bag volume (in cubic feet)Formula: Volume = πr^2h,