How Much Concrete for an 8x8 Slab?
Concrete needed
0.87 cubic yards
An 8 by 8 foot 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.
- Length8 ft
- Width8 ft
- Thickness4 in
- Waste allowance10 %
Concrete needed0.87 cubic yards
| Volume | 21.3 cu ft |
|---|---|
| Cubic yards before waste | 0.79 |
| Cubic yards with 10% waste | 0.87order to this number |
| Order in quarter yards | 1 cu yd |
| 60 lb bags, if bagging it | 53 |
| 80 lb bags, if bagging it | 40 |
The material list this produces
| Ready mix concrete, cubic yards | 1 |
|---|---|
| Rebar or mesh, sq ft of slab | 64 |
| Form lumber, linear ft | 32 |
Thickness compared
Thickness is the one number on this page worth arguing about, so here is the same slab at each of the usual four.
| Thickness | Concrete needed |
|---|---|
| 4 in | 0.87 cubic yards |
| 5 in | 1.09 cubic yards |
| 6 in | 1.3 cubic yards |
| 8 in | 1.74 cubic yards |
What else matters here
Point eight seven of a yard. This is the exact size where the answer flips, because most ready mix suppliers set their minimum at one yard and this slab sits just under it.
Order the full yard. The difference between 0.87 and 1.0 is small money and it removes the short load fee, the risk of coming up short on the last corner, and the fifty three bags of sixty pound mix that are the alternative. Fifty three bags is a full day and a sore back.
Eight feet is also where control joints start to matter. A four inch slab wants a joint every eight to ten feet, so an 8 by 8 is right at the limit: one joint across the middle, cut within the first day while the concrete is still green, or tooled in during the finish.
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 8x8 slab?
About 0.87 cubic yards at 4 inches thick with waste, so order one yard. In bags it is around 53 sixty pound or 40 eighty pound.
Is an 8x8 slab a bag job or a truck job?
A truck job if you can get one for the minimum. Fifty three bags is a full day of mixing and carries a real risk of a cold joint.
Does an 8x8 slab need a control joint?
Yes, one across the middle. Four inch slabs want a joint every eight to ten feet, and 8 feet is at the top of that range.
The concrete calculator takes any dimensions you like and hands back the same list.