About this calculator
Concrete for deck footings, pergola piers, porch columns and pad foundations. Works for round tube formers 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
- 300 mm
- Height / depth
- 900 mm
- Number of piers
- 8
- Supply as
- Pre-mixed bags
- Bag size
- 20 kg
- Waste allowance
- 10%
the result is:
- Concrete needed
- 0.56 m³
- Per pier
- 0.06 m³
- Premix order (to 0.2 m³)
- 0.6 m³
- 20 kg bag
- 59 bags
- Approx. wet weight
- 1.34 t
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.
- Footings must sit on firm natural ground. On reactive clay sites, depth and size come from the engineer or AS 2870. Frost only matters in alpine areas.
Common questions
How many bags for a 300 mm pier?
A 300 mm × 900 mm round pier holds about 0.064 m³, roughly eight 20 kg bags with waste.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the NCC and Australian Standards before ordering.