About this calculator
Estimate concrete for strip foundations under walls, checked against the SANS 10400-H minimum sizes. Enter the total length of all runs, then the width and depth.
How it’s calculated
Volume = total length × width × depth, plus waste. For a rectangular building, the total length is roughly the perimeter. Measure along the centreline of the footing so the corners aren’t counted twice.
Worked example
With these inputs:
- Total footing length
- 18 m
- Wall on the footing
- Load-bearing or free-standing masonry
- Width
- 600 mm
- Thickness
- 200 mm
- Supply as
- Mix on site (cement, sand and stone)
- Concrete mix
- Low strength (house foundations)
- Waste allowance
- 10%
the result is:
- Concrete needed
- 2.38 m³
- Net volume
- 2.16 m³
- Plan area
- 10.8 m²
- Cement (50 kg bags)
- 14 bags
- Concrete sand
- 1.54 m³
Tips from the trade
- Dug trenches are rarely neat. Allow 10–15% waste, or more in sandy soil where the sides slump.
- SANS 10400-H: strip foundations at least 200 mm thick, and at least 600 mm wide under load-bearing or free-standing masonry walls (400 mm under internal non-load-bearing walls). Where a footing steps down, the higher part overlaps the lower by at least its own thickness.
- Order ready-mix with a little spare. Running short on a footing pour leaves a cold joint.
Common questions
How do I measure a footing perimeter?
Add the centreline lengths of every wall run. For a simple rectangle, that is 2 × (length + width) minus 4 × the footing width.
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.