About this calculator
Concrete for deck footings, pergola piers, porch columns and pad foundations. Works for round cardboard form tubes and square dug pads.
How it’s calculated
Round: π × (diameter ÷ 2)² × height. Square: side A × side B × height. Multiply by the number of piers, then add waste.
Worked example
With these inputs:
- Shape
- Round (tube)
- Diameter
- 12 in
- Height / depth
- 4 ft
- Number of piers
- 8
- Supply as
- Pre-mixed bags
- Bag size
- 80 lb
- Waste allowance
- 10%
the result is:
- Concrete needed
- 1.02 cu yd
- Per pier
- 3.1 cu ft
- Ready-mix order (to ¼ yd)
- 1.25 cu yd
- 80 lb bag
- 47 bags
- 60 lb bag
- 62 bags
Tips from the trade
- A bell or spread footing at the base adds volume. Add it as a separate square pad calculation.
- Dug holes are wider than the tube. If you pour straight into the ground, measure the hole, not the tube size.
- Footing depth must reach below your local frost line.
Common questions
How many bags for a 12-inch pier?
A 12" × 48" tube holds about 3.1 cu ft, roughly six 80 lb bags with waste.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and local building codes before ordering.