Concrete & Mortar Calculator

How many bags of ready-mix concrete or mortar do you need for any project? Calculate by volume — posts, slabs, foundations, pointing.

Project type

Length (m)

Width (m)

Depth / thickness (mm)

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Fill in the details to get your calculation.

Rapid-set post fix sets in 5 minutes — no mixing required, ideal for fence posts.

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How This Is Calculated

Volume is calculated as length × width × depth for slabs, or post hole volume (π × radius² × depth) for posts. Bagged concrete yields approximately 12L of mixed concrete per 25kg bag. For volumes over 0.5m³, ready-mixed concrete from a truck is usually cheaper per m³ than bagged.

For a garden path or patio slab, a 1:2:3 mix (1 part cement : 2 parts sharp sand : 3 parts aggregate) or ready-mix C20/C25 concrete is standard. For foundations, use 1:2:4 or C25. For post holes, a pre-bagged rapid-setting concrete is convenient — no mixing, just add water. Avoid using general-purpose mortar mix for structural applications.