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
- 12 m
- Wall height
- 2.4 m
- Thickness
- 200 mm
- Openings (doors/windows) area
- 0 m²
- Supply as
- Pre-mixed bags
- Bag size
- 25 kg
- Waste allowance
- 10%
the result is:
- Concrete needed
- 6.34 m³
- Wall face area
- 28.8 m²
- Net volume
- 5.76 m³
- Ready-mix order (to 0.25 m³)
- 6.5 m³
- 25 kg bag
- 551 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 Regulations before ordering.