Multi-Area Concrete Calculator
Short answer: add each section's volume, then divide by 27. A 10 × 10 ft slab plus a 12 × 12 ft slab, both 4 in thick, need 3.01 cubic yards together.
Calculate all your sections
Enter up to four sections. Leave unused sections blank — a section with only some fields filled will ask you to complete it.
How the calculation works
Each section is length × width × thickness ÷ 12 (cubic feet). Sections are added together, divided by 27 for cubic yards, then the waste allowance is applied once to the total.
Worked example: 10 × 10 ft at 4 in (33.33 cu ft) plus 12 × 12 ft at 4 in (48 cu ft) = 81.33 cu ft = 3.01 cubic yards, or 3.31 with 10% waste.
When to use it
| Project | Sections |
|---|---|
| Driveway + walkway | Two slabs, different thicknesses |
| Patio + shed base | Two pads, same or different sizes |
| Several footings | Identical footing, repeated — or use the footing calculator count |
| Pour in stages | One section per stage |
If every section is identical, the footing calculator's count field is quicker.
Frequently asked questions
How do I calculate concrete for multiple slabs?
Calculate each slab separately (length × width × thickness ÷ 27), add the cubic yards together, then add 5–10% waste once to the total.
Can I add different thicknesses together?
Yes — volume is volume. Enter each section with its own thickness and the calculator adds the cubic feet before converting to yards.
Should waste be added per section or to the total?
To the total is fine and is what this calculator does — adding it per section double-counts the rounding.