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
- Mix on site (cement, sand and stone)
- Concrete mix
- Low strength (house foundations)
- Waste allowance
- 10%
the result is:
- Concrete needed
- 0.56 m³
- Per pier
- 0.06 m³
- Cement (50 kg bags)
- 4 bags
- Concrete sand
- 0.36 m³
- Stone (19 mm)
- 0.36 m³
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 below the topsoil. On clay or other poor ground, the size and depth come from an engineer.
Common questions
How many bags for a 300 mm pier?
A 300 mm × 900 mm round pier holds about 0.064 m³. At the low-strength mix, one 50 kg bag of cement makes about 0.17 m³ of concrete, enough for two piers with a little to spare.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.