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)

If your pour is a shape this calculator does not cover — a cone, a sphere, or an L- or T-shaped footprint split into two rectangular sections — our general volume calculator for m³ and litres will work out the total volume for you.

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. A 5-10% allowance is a common trade rule of thumb recommended by ready-mix suppliers; for trenches in rough or over-excavated ground, 15-20% is safer. This is general practice rather than a figure fixed by any single standard — always follow your supplier’s advice.

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.