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Foundation intentHow much concrete do I need for a foundation?
Foundations are often strip footings or stepped runs, so the estimate is best handled by breaking the layout into rectangular sections.
Best for
- Strip foundations
- Stepped footings
- Small foundation runs
Worked example
A foundation with two straight sections
If the foundation changes depth, split it into sections and add the volumes together before applying waste.
Example
Section A: 12 m × 0.6 m × 0.3 m = 2.16 m3. Section B: 8 m × 0.6 m × 0.35 m = 1.68 m3. Total = 3.84 m3. With 5 percent waste, the adjusted order volume is 4.03 m3.
Formula
Volume = sum of rectangular sections
Adjusted volume = volume × (1 + waste / 100)
How to use it
Foundation planning notes
Break into sections
Different widths or depths should be treated as separate rectangles.
Use the real section
The concrete volume is based on the actual poured section, not just the wall above it.
Waste factor
Add allowance for spill, irregular trench bottoms, and setup loss.
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