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
- 25 kg
- Waste allowance
- 10%
the result is:
- Concrete needed
- 0.56 m³
- Per pier
- 0.06 m³
- Ready-mix order (to 0.25 m³)
- 0.75 m³
- 25 kg bag
- 49 bags
- 20 kg bag
- 59 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.
- Footings must sit on firm ground below frost depth, usually at least 450–600 mm in the UK, and deeper in clay or near trees.
Common questions
How many bags for a 300 mm pier?
A 300 mm × 900 mm round pier holds about 0.064 m³, roughly six 25 kg bags with waste.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.