Cylinder deck footings and Sonotube forms: pick diameter and depth, set how many piers, add a waste margin, get cubic feet, cubic yards, and bag counts.
Tube / footing diameter
Concrete needed
13.82 cu ft
0.512 cu yd · one footing 3.14 cu ft
- 40 lb bags (0.3 cu ft)
- 47
- 60 lb bags (0.45 cu ft)
- 31
- 80 lb bags (0.6 cu ft)
- 24
Formula
Volume of one cylinder (inches): V = π × (diameter ÷ 2)² × depth ÷ 1728 cubic feet. Multiply by the number of footings, then by (1 + waste ÷ 100). Cubic yards = cubic feet ÷ 27. Bag counts use common bagged-concrete yields of 0.30 / 0.45 / 0.60 cu ft for 40 / 60 / 80 lb bags; round up.
Example: four 12" tubes, 48" deep, 10% waste → one footing ≈ 3.14 cu ft; four ≈ 12.57 cu ft; with waste ≈ 13.82 cu ft (≈ 0.512 cu yd) → about 47×40 lb, 31×60 lb, or 24×80 lb bags.