Concrete Calc Pro Select. This easy to use Concrete Calculator supports both rectangle and round shapes and will provide: Concrete Rectangle. Total cubic yards. Total cubic feet. Total cubic meters. Total area (sq ft). # of 60 or 80 pound Premixed bags. # of 25k or 50k Premixed bags. # 2500psi, 3000psi or 3500psi Portland bags. Total feet/meters of rebar.