Concrete calculator
Enter your slab dimensions to get cubic yards (for ready-mix) and bag counts (for premix). Includes a printable shopping list.
Material Totals
1 cu yd = 27 cu ft. One 80lb bag covers ~0.6 cu ft; one 60lb bag ~0.45 cu ft. For pours over ~1 cu yd, ready-mix delivery is usually more economical.
Printable Shopping List
Generated by BuildTotals.com | 7/1/2026 | buildtotals.com/tools/concrete-calculator
Estimates include 10% waste factor. Confirm with your supplier before purchasing.
Sample trace: 10ft x 12ft slab, 4in depth
- Volume = 10 x 12 x (4/12) = 40 cu ft
- With 10% waste = 40 x 1.10 = 44 cu ft
- Cubic yards = 44 / 27 = 1.63 cu yd
- 80lb bags (0.6 cu ft/bag) = ceil(44 / 0.6) = 74 bags
- 60lb bags (0.45 cu ft/bag) = ceil(44 / 0.45) = 98 bags
Above 1-2 cu yd, ready-mix delivery is usually more economical. Contact a local supplier for pricing.
Related projects
When to hire a contractor
Most DIYers can handle slabs under 2 cubic yards (a typical 10x12 patio) with careful preparation and a rented mixer or pre-bagged concrete. For larger pours or anything structural, consider consulting a licensed concrete contractor.
How to use the concrete calculator
Enter length, width, and depth. The depth is almost always measured in inches - a standard patio slab is 4 inches, a driveway is 4-6 inches, and a structural footing is typically 8-12 inches.
Set the waste factor. For a simple rectangular slab, 10% is usually enough. For irregular shapes, step footings, or pours in cold weather (where you may need to discard partially set material), use 15%.
Frequently asked questions
How many 80lb bags of concrete do I need for a 10x12 slab at 4 inches?
A 10x12 slab at 4 inches deep is 40 cubic feet. With a 10% waste factor that is about 44 cubic feet. At 0.6 cubic feet per 80lb bag, you need about 73 bags. The calculator above will trace this exactly.
How do I convert cubic feet to cubic yards?
Divide by 27. There are 27 cubic feet in one cubic yard. For a 10x12 slab at 4 inches: 10 x 12 x (4/12) = 40 cu ft. Then 40 / 27 = 1.48 cu yd (before waste).
When should I order ready-mix instead of bags?
For pours under about 1 cubic yard (27 cu ft), premix bags are practical. Above that, a ready-mix truck is faster and typically cheaper per cubic yard. The break-even is around 50-80 bags depending on your local ready-mix delivery minimum.
What waste factor should I use for concrete?
10% is standard for most slabs. If your forms are irregular, if you are filling block or column forms, or if the sub-base is uneven, use 15%. The calculator lets you set any waste percentage.