About this calculator
Concrete for formed walls such as foundation walls, retaining walls and stem walls. Window and door openings are subtracted.
How it’s calculated
Volume = (length × height − openings) × thickness, plus waste.
Worked example
With these inputs:
- Wall length
- 40 ft
- Wall height
- 8 ft
- Thickness
- 8 in
- Openings (doors/windows) area
- 0 sq ft
- Supply as
- Pre-mixed bags
- Bag size
- 30 kg
- Waste allowance
- 10%
the result is:
- Concrete needed
- 6.65 m³
- Wall face area
- 320 sq ft
- Net volume
- 6.04 m³
- Ready-mix order (to 0.25 m³)
- 6.75 m³ (8.83 cu yd)
- 30 kg bag
- 475 bags
Tips from the trade
- Formwork bows slightly under load. 5–8% waste covers that plus the pump line.
- Plan pump access for walls taller than you can reach from a chute.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the building code adopted in your province before ordering.