The physical relationship
Strip-footing volume is length × width × depth. Pier volume is count × π × radius² × depth for round piers, or count × length × width × depth for square piers. The calculator adds the selected waste percentage after summing those separate shapes. It is a quantity take-off, not a footing design.
A checked case
A strip footing 18 m long, 0.45 m wide, and 0.30 m deep has 18 × 0.45 × 0.30 = 2.43 m³. Four round piers 0.30 m in diameter and 0.90 m deep add 4 × π × 0.15² × 0.90 = 0.254 m³. Together they are 2.684 m³. With 8% waste, 2.684 × 1.08 = 2.899 m³, so an order must be rounded according to the supplier's delivery increment.
Useful planning use
Use it to check a drawing take-off, compare ready-mix delivery quantities, or separate a continuous strip from discrete piers instead of hiding both in one guessed slab volume.
Failure modes in this measurement
Depth in centimetres must become metres before multiplication; 300 cm is not a 0.30 m footing. Excavations are often wider or irregular, but ordering to a rough excavation rather than the specified concrete section wastes material and can conceal a design error. Circular piers need radius, half the diameter. Wet ground, rock, sloping trenches, reinforcement displacement, and a pump's residual volume can all change the practical order.
What makes this quantity different
The basic Concrete Calculator returns only the rectangular volume of one slab. This page combines a strip footing with optional piers and a visible allowance, making each component auditable. It does not calculate mix strength, reinforcement, bearing capacity, frost depth, curing, or excavation safety.
Field check before acting
Read dimensions from the approved foundation detail and keep a list of every separate run. Exclude overlaps only when the drawing shows one continuous pour rather than two volumes occupying the same space. Ask the supplier about minimum load, tolerance, and washout before ordering. On site, verify form dimensions and depth before the truck arrives; adding water to make placement easier can change concrete properties.
Limits of the model
Foundation dimensions and concrete specification are structural matters. Soil bearing, drainage, frost, reinforcement, loads, and local code can require engineered details. The result is only a material-volume estimate and must not replace those requirements.