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 | 6/13/2026 | 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. If you just moved into your new home, TallyClose can help you understand what closing costs you paid and what to expect next time.
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.