How Much Concrete for a 12x12 Slab?
Concrete needed
1.96 cubic yards
A 12 by 12 slab at four inches, with ten percent on top for waste.
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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.
- Length12 ft
- Width12 ft
- Thickness4 in
- Waste allowance10 %
Concrete needed1.96 cubic yards
| Volume | 48 cu ft |
|---|---|
| Cubic yards before waste | 1.78 |
| Cubic yards with 10% waste | 1.96order to this number |
| Order in quarter yards | 2 cu yd |
| 60 lb bags, if bagging it | 118 |
| 80 lb bags, if bagging it | 88 |
The material list this produces
| Ready mix concrete, cubic yards | 2 |
|---|---|
| Rebar or mesh, sq ft of slab | 144 |
| Form lumber, linear ft | 48 |
Thickness compared
The same slab at four thicknesses.
| Thickness | Concrete needed |
|---|---|
| 4 in | 1.96 cubic yards |
| 5 in | 2.44 cubic yards |
| 6 in | 2.93 cubic yards |
| 8 in | 3.91 cubic yards |
What else matters here
A hundred and forty four square feet at four inches lands almost exactly on two cubic yards with waste, which makes this an easy one to order and an easy one to check.
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 many yards of concrete for a 12x12 slab?
1.78 cubic yards of volume, 1.96 with a ten percent waste allowance, so you order two yards. At six inches it is just under three.
How many 80 lb bags for a 12x12 slab?
Around 88 at four inches thick with waste in. At almost two yards that is past the one cubic yard where ready mix becomes the cheaper option.
The concrete calculator takes any dimensions you like and hands back the same list.