Concrete Volume Calculator

A 10×10 foot slab at 4 inches thick has a volume of 0.929 m³ (approximately 1.22 cubic yards). With a standard 10% waste factor that becomes approximately 1.02 m³. At the standard yield of 0.012 m³ per 25 kg bag you would need approximately 85 bags of 25 kg ready-mix. Enter these exact dimensions in the Slab tab above for a precise result with your chosen thickness and mix grade.

These designations refer to the compressive strength of the concrete after 28 days, measured in megapascals. C20 achieves 20 MPa and suits paths and non-structural slabs. C25 achieves 25 MPa and is the standard residential specification for driveways and foundations. C30 achieves 30 MPa and is used where greater strength is needed — garage floors, columns, and footings for heavier structures. For most residential DIY projects, C25 is the appropriate specification.

Use the Column tab, select Round, and enter the diameter and height. The formula used is π × r² × h, where r is the radius (half the diameter). For example, a 300 mm diameter column 2.4 metres tall requires π × 0.15² × 2.4 = 0.170 m³ of concrete. Enter the number of columns to get the combined total for all piers on your project.

10% is the standard allowance for most residential pours on a flat prepared subbase. Use 15% for strip footings in rough-cut trenches, irregular-shaped areas, or any pour where you expect higher losses. Use 5% only for very precise pours into smooth-sided formwork with minimal handling, such as precast column forms. It is almost always cheaper to order slightly more than to arrange a second delivery.