Concrete Volume Calculator — How Much Concrete Do I Need?

This calculator computes the volume of concrete needed based on the shape and dimensions you enter. It supports rectangular slabs, circular slabs, and trench/strip foundations.

The formulas

• Rectangular slab: Volume = Length × Width × Depth
• Circular slab: Volume = π × (Diameter/2)² × Depth
• Trench/strip: Volume = Length × Width × Depth (same as rectangular, entered as trench dimensions)

Conversion to delivery quantities

Ready-mix lorries in the UK typically carry 6m³ per load. For smaller jobs, 20kg premix bags each produce approximately 0.009 m³ of concrete.

The 10% wastage allowance accounts for spillage, uneven ground, and over-excavation. This is the standard recommendation from most UK concrete suppliers and aligns with NHBC guidance for domestic construction.

UK Building Regulations

For structural foundations, refer to Building Regulations Approved Document A (Structure) for minimum concrete depths and widths. Strip foundations for standard domestic walls typically require a minimum of 225mm concrete depth, with trench depths varying by soil type.