About this calculator
Concrete for formed walls such as foundation walls and retaining 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
- Mix on site (cement, sand and stone)
- Concrete mix
- Medium strength (house floors, footpaths, driveways)
- Waste allowance
- 10%
the result is:
- Concrete needed
- 6.34 m³
- Wall face area
- 28.8 m²
- Net volume
- 5.76 m³
- Cement (50 kg bags)
- 49 bags
- Concrete sand
- 3.93 m³
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 SANS 10400 (the National Building Regulations) and your local municipality before ordering.