Concrete guide
Concrete waste guide
Waste is not the same for every pour. Small slabs and simple footings may need only a modest allowance, while awkward shapes or long transport runs often need more.
Small slabs
A typical allowance is modest because the geometry is simple and the pour is easy to control.
Long footings
Allow a bit more when the pour is long, the forms are uneven, or the trench depth varies.
Irregular shapes
Split the shape into rectangles and apply a slightly larger allowance if the edges are hard to set out.
Example
Waste example
A clean slab may use 5 to 7 percent waste.
A footing with multiple steps or a tricky pour might need 8 to 10 percent instead.