Concrete Footing Calculator
About Concrete Footing Calculator
Concrete Footing Calculator sizes the pour for strip footings and foundation trenches, where the trench run is the length, the trench width is the width and the pour depth is the depth. A 10 m run of footing at 450 mm wide and 300 mm deep holds 1.35 m3, or 1.485 m3 once 10 percent waste is added. A 30 ft run at 18 inches wide and 12 inches deep works out to about 1.83 cubic yards with waste. Footings are the pour where a waste allowance earns its keep, because excavated trench walls are never perfectly straight and soft spots swallow noticeably more concrete than the drawing suggests, so 15 percent is a reasonable setting for hand dug trenches in loose ground. For a building perimeter, add the length of every trench run first and enter that total as the length rather than calculating each wall separately. Footing width and depth are set by the ground conditions and the load above, so take them from the approved drawings or building control notice rather than estimating them.
How to use Concrete Footing Calculator
- Choose metric or imperial input
- Enter length, width, and depth of your slab
- See volume and bag count in both metric and imperial instantly
Frequently Asked Questions
- How do I calculate concrete for footings?
- Multiply total trench length by trench width by pour depth. A 10 m run at 450 mm wide and 300 mm deep is 10 x 0.45 x 0.3 = 1.35 m3. For a full perimeter, add all trench runs together and enter the total as the length input.
- How deep should a footing be?
- Depth is set by ground conditions and local building regulations, not by a rule of thumb. In the UK, 900 mm to 1 m below ground level is common on clay to stay below seasonal movement, with a concrete pour depth of 200 to 300 mm within that trench. Always work from approved drawings.
- How much waste should I allow on footings?
- More than on a slab. Trench walls are rough, and soft spots absorb extra concrete, so 15 percent is sensible for hand dug trenches. Running short part way through a footing pour creates a cold joint in a structural element, which is worth paying to avoid.
- Can I calculate footings for a whole house perimeter?
- Yes. Add every trench run to get one total length, then enter your standard trench width and pour depth. If sections use different widths, calculate each width group separately and add the volumes together.
- Does the calculator work for pad footings?
- Yes, as long as the pad is rectangular. Enter the pad length, the pad width and the pour depth, then multiply the result by the number of identical pads. Circular pier holes are not rectangular, so this calculator does not cover them.
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