PROJECT GUIDE
How Much Concrete Do I Need?
The answer depends on the project dimensions and thickness. For a simple rectangular slab, you can calculate the basic volume with a short formula and then check the practical ordering quantity.
The basic formula
Concrete volume = length × width × thickness. Use feet for all three dimensions. If thickness is given in inches, divide it by 12 to convert it to feet. Then divide cubic feet by 27 to convert to cubic yards.
A quick example
For a 10 ft × 12 ft area at 4 inches thick, the volume is 12 × 10 × (4 ÷ 12) = 40 cubic feet. Divide 40 by 27 and the result is about 1.48 cubic yards before any allowance.
Why the order quantity may be higher
The mathematical volume describes a geometric shape. A real pour can have uneven subgrade, small measuring errors, spillage or other losses. Supplier minimums and delivery increments can also affect what you actually order.
For irregular shapes
Break the project into rectangles or other simple shapes, calculate each part separately and add the volumes. If the geometry is complex or the work is structural, use the project drawings or a qualified professional to establish the required quantity.
Use the calculator
Enter length, width and thickness in the Concrete Calculator. The result shows the basic volume and a planning quantity after the selected allowance.
Use the calculator
Ready to run the numbers? Use the BuildPlanTools calculator, then compare the estimate with the product label, supplier information and project requirements.
These estimates are for general planning. Product specifications, site conditions, local requirements and professional recommendations should take priority where applicable.