How Much Concrete for an 8x12 Slab?
Concrete needed
1.3 cubic yards
An 8 by 12 foot slab at four inches, with ten percent on top for waste.
It does not stop at a number.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Length8 ft
- Width12 ft
- Thickness4 in
- Waste allowance10 %
Concrete needed1.3 cubic yards
| Volume | 32 cu ft |
|---|---|
| Cubic yards before waste | 1.19 |
| Cubic yards with 10% waste | 1.3order to this number |
| Order in quarter yards | 1.5 cu yd |
| 60 lb bags, if bagging it | 79 |
| 80 lb bags, if bagging it | 59 |
The material list this produces
| Ready mix concrete, cubic yards | 1.5 |
|---|---|
| Rebar or mesh, sq ft of slab | 96 |
| Form lumber, linear ft | 40 |
Thickness compared
The same slab at four thicknesses.
| Thickness | Concrete needed |
|---|---|
| 4 in | 1.3 cubic yards |
| 5 in | 1.63 cubic yards |
| 6 in | 1.96 cubic yards |
| 8 in | 2.61 cubic yards |
What else matters here
About 1.3 yards, which is past the one yard where ready mix becomes the cheaper option.
What this calculator assumes
- One cubic yard is 27 cubic feet. A 4 inch slab is one third of a foot thick, not 4.
- A 60 lb bag yields about 0.45 cubic feet and an 80 lb bag about 0.60. Bags are for small pours only; past about one cubic yard, ready mix is cheaper and far less work.
- Ready mix is usually sold in quarter yard steps with a short load fee below one yard.
Questions people ask
How much concrete for an 8x12 slab?
About 1.3 cubic yards at 4 inches thick with a ten percent waste allowance.
Different numbers?
The concrete calculator takes any dimensions you like and hands back the same list.