Concrete Footing Calculator
Calculate concrete for strip footings or a set of identical pad footings.
Formula
Volume of one footing = Length × Width × Depth. Multiply by the number of footings, then add wastage.
- One footing (m³) = L × W × D
- Net (m³) = One footing × Quantity
- Total (m³) = Net × (1 + wastage % ÷ 100)
Worked example
A continuous strip footing 20 m long, 600 mm wide and 450 mm deep, at 10% wastage.
- Convert: 600 mm = 0.6 m, 450 mm = 0.45 m
- Volume = 20 × 0.6 × 0.45 = 5.40 m³
- Wastage = 5.40 × 0.10 = 0.54 m³
- Total = 5.94 m³
Order approximately 6 m³.
Assumptions and limitations
- The footing has a constant rectangular cross-section. Stepped footings must be split into segments and each calculated separately.
- For a strip footing running around a building, the length entered should be the centreline length, otherwise corners are double-counted or missed.
- This tool calculates quantity only. It does not size the footing, check bearing pressure, or verify any structural requirement.
What this calculator does not do
- Does not size the footing. Width, depth and reinforcement come from a structural design based on the loads and the ground, not from a quantity calculator.
- Does not check bearing capacity, settlement, frost depth or founding level.
- Does not include blinding, formwork, starter bars, or excavation for the footing. Those are separate quantities.
Practical tips
- Measure the centreline of a closed loop of strip footing. Using the external perimeter over-counts each corner by roughly one footing width.
- In loose or collapsing ground, consider whether trench sheeting changes the poured width — the concrete fills whatever the excavation actually is.
- Pad footings of different sizes should be run as separate calculations and added, not averaged.
Frequently asked questions
How do I calculate concrete for a strip footing?
Multiply the centreline length by the width by the depth, all in metres, then add a wastage allowance. For footings poured against soil, allow 10–15% rather than the 5% typical of formed work.
Should I use the centreline or the outside perimeter?
The centreline. If you use the outside perimeter on a closed loop, you count each corner twice — on a small building that error is easily a full cubic metre.
Why is footing wastage higher than slab wastage?
Footings are usually poured straight against excavated ground. The trench is never exactly the designed width, and soft spots over-break, so the concrete fills more than the drawn section.
Does this calculator design the footing?
No. It calculates quantity only. Footing dimensions come from a structural design based on loads and ground bearing capacity, and must be taken from your project drawings.
Related calculators
- Concrete Volume Calculator Work out the volume of concrete needed for a rectangular pour, with an allowance for wastage.
- Concrete Slab Calculator Size a floor or ground slab: volume, ready-mix load, weight and area, including an edge thickening if there is one.
- Excavation Calculator Calculate excavation volume in bank measure and the swelled volume that has to be hauled away.
- Backfill Calculator Calculate backfill volume around a structure and the material you need to import, using whichever compaction convention your source figure came from.
- Rebar Weight Calculator Calculate the weight of reinforcement bars from diameter, length and quantity.
Estimating tool, not a design. This calculator works out quantities from the dimensions you enter. It does not size any structural member, verify a design, or confirm compliance with any building code. Check every result against your project specification and applicable local standards, and involve a qualified engineer where the work requires one.