Concrete Calculator
Estimate how much concrete you need for your project, whether you are setting fence posts, laying a shed base, pouring a patio, building a garden path, or digging footings. Get quantities for ready-mix bags or individual materials (cement, sand, aggregate) to mix your own.
Project Details
Choose your project type and enter the dimensions.
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About This Calculator
Our concrete calculator helps you estimate materials for your project. Choose your project type and enter the dimensions to get an approximate volume of concrete needed, including a 10% waste allowance for spillage and over-filling.
The calculator gives you two options: the number of ready-mix 20kg bags (such as Blue Circle or Postcrete), or the individual quantities of cement, sharp sand, and 20mm aggregate to mix your own using a standard C20 mix ratio (1:2:3 by volume).
When to Use Ready-Mix vs Mixing Your Own
For small jobs like fence posts (under 0.1m³), ready-mix bags are convenient and quick. For larger projects like shed bases and patios, mixing your own from bulk materials is significantly cheaper. As a rough guide, anything over 0.3m³ is worth mixing yourself or ordering volumetric concrete from a local supplier.
These calculations are estimates based on standard manufacturer coverage rates. Actual quantities may vary depending on surface conditions, wastage, and application technique. Always verify quantities with your supplier before purchasing.