How Much Concrete Do I Need?
How much concrete you need is the volume of your project in cubic yards: length times width times thickness in feet, divided by 27. A 10 by 10 foot slab at 4 inches thick needs about 1.23 cubic yards, or roughly 56 of the 80-pound bags. The table below covers common sizes, and the calculator works out your exact figure.
| Slab size | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 8 x 8 ft | 0.79 | 36 | 48 |
| 10 x 10 ft | 1.23 | 56 | 74 |
| 12 x 12 ft | 1.78 | 80 | 107 |
| 16 x 16 ft | 3.16 | 142 | 190 |
| 20 x 20 ft | 4.94 | 222 | 297 |
| 24 x 24 ft | 7.11 | 320 | 427 |
| 30 x 30 ft | 11.11 | 500 | 667 |
Get your exact number
Calculate your exact amount with the concrete calculatorHow Do You Calculate Concrete Needed?
To calculate concrete, multiply length by width by thickness in feet to get cubic feet, then divide by 27 for cubic yards. A 12 by 12 foot slab at 4 inches (0.33 feet) thick is 48 cubic feet, or 1.78 cubic yards. For bagged concrete, each 80-pound bag yields about 0.6 cubic feet, so divide the total cubic feet by 0.6. The table above does this for common sizes; the calculator handles any dimensions.
How Many Bags of Concrete Make a Yard?
It takes about 45 of the 80-pound bags, 60 of the 60-pound bags, or 90 of the 40-pound bags to make one cubic yard of concrete. Bagged concrete is practical for small jobs like posts and small pads, but for anything over about half a yard, ready-mix delivery is usually cheaper and easier than mixing dozens of bags. The calculator shows both bag counts and yards so you can decide.
Related answers
Frequently asked questions
- How much concrete do I need for a 10x10 slab?
- A 10 by 10 foot slab at 4 inches thick needs about 1.23 cubic yards, or roughly 56 of the 80-pound bags.
- How many bags of concrete make a yard?
- About 45 of the 80-pound bags, 60 of the 60-pound bags, or 90 of the 40-pound bags per cubic yard.
- How much concrete for a fence post?
- A typical 4x4 post in a hole about 8 inches wide and 2 feet deep needs 1 to 2 of the 50 or 60-pound bags.