The amount of concrete you need equals the volume of the space you’re filling. Calculate that volume, add 10% for waste, then convert to cubic yards or cubic metres depending on your supplier. Most residential projects \u2014 slabs, footings, driveways \u2014 fall between 1 and 10 cubic yards (0.76\u20137.65 m\u00b3). Get that number wrong and you’re either stopping work to reorder or paying for concrete you can’t use.<\/p>\n\n\n\n
The formula is the same for every project: Volume = Length \u00d7 Width \u00d7 Thickness<\/strong>. Use consistent units throughout. For slabs and flatwork, thickness in imperial is usually expressed in inches, which must be converted to feet before multiplying (divide inches by 12). In metric, thickness in millimetres must be converted to metres (divide by 1000).<\/p>\n\n\n\n Worked example \u2014 imperial: A slab 12 ft \u00d7 20 ft \u00d7 4 in thick = 12 \u00d7 20 \u00d7 (4\/12) = 80 cu ft. Divide by 27 to convert to cubic yards: 80 \u00f7 27 = 2.96 cubic yards<\/strong>. Add 10% waste: 3.26 cubic yards \u2014 order 3.5 yds to be safe.<\/p>\n\n\n\n Worked example \u2014 metric: A slab 3.6 m \u00d7 6 m \u00d7 100 mm thick = 3.6 \u00d7 6 \u00d7 0.1 = 2.16 cubic metres<\/strong>. Add 10% waste: 2.38 m\u00b3. Round up to 2.5 m\u00b3 when ordering.<\/p>\n\n\n\n Use the Concrete Slab Calculator<\/a> to handle the arithmetic automatically \u2014 input length, width, and thickness in any unit and it returns cubic yards, cubic feet, cubic metres, and bag counts simultaneously.<\/p>\n\n\n\n Different projects have standard thickness requirements that directly drive volume. The table below shows representative scenarios across the most common project types. These are real-world dimensions, not minimums.<\/p>\n\n\n\nConcrete volumes for common project types<\/h2>\n\n\n\n