12 × 12 slab by thickness
Every figure includes 10% waste. Bag counts use the manufacturers' stated yields (0.6 cu ft per 80 lb bag, 0.45 per 60 lb).
| Thickness | Cubic yards | 80 lb bags | 60 lb bags | Bags cost | Ready-mix cost |
|---|---|---|---|---|---|
| 4 in | 1.96 | 89 | 118 | $534 to $712 | $304 to $522 |
| 5 in | 2.44 | 110 | 147 | $660 to $880 | $368 to $614 |
| 6 in | 2.93 | 132 | 176 | $792 to $1,056 | $431 to $707 |
| 8 in | 3.91 | 177 | 235 | $1,062 to $1,416 | $558 to $893 |
Past a yard and a half, most people who price both end up calling the plant. One 12 × 12 pour is a long day for two people with bags.
Building a 12 × 12 slab
The carport is the catch at this size. A patio or shed is fine at 4 inches with wire mesh. The moment a car parks on it, go to 5 inches with #4 rebar on a 24-inch grid, set on chairs at mid-depth, over 4 inches of compacted gravel; the thickness table above has the 5-inch numbers, and the difference is about half a cubic yard. If the slab butts against the house, put a 1/2-inch expansion strip against the foundation so the slab can move without pushing on the wall, and slope it 1/8 inch per foot away from the house, about 1.5 inches across 12 feet.
Pour day at this size
At 144 square feet, screed with a 14-foot straightedge so one pass clears the forms, or set a temporary screed rail down the middle and pour in two halves. Cut or tool one control joint across the center within the first day; a 12 × 12 at 4 inches is right at the edge of what cracks on its own. Three people make this comfortable: one on the chute or wheelbarrow, two screeding.
Joint spacing and depth follow ACI 302.1R (joints every 24 to 36 times the slab thickness, cut one quarter deep); anchor bolt spacing follows IRC R403.1.6; load figures come from manufacturers' published weights. Local code wins where it differs.
Having it poured instead
Contractors charge about $6 to $12 per square footfor a finished 4-inch slab in 2026, which puts a 12 × 12 slab at$864 to $1,728 installed. That covers forming, gravel base, pour, and finish; thicker slabs, reinforcement, and site prep on sloped or hard-to-reach ground push it toward the top of the range.
How we get these numbers
Volume is length × width × thickness in cubic feet, divided by 27, plus 10% waste. Bag yields come from the manufacturers' technical data sheets. Ready-mix runs $130 to $190per yard delivered, with a $50 to $150short-load fee under 5 yards at most plants. Prices refreshed at least twice a year (last: September 2026). Sources:
- Concrete Network: Concrete Prices 2026, How Much Is a Yard of Concrete?
- Angi: Concrete Cost Per Yard (2026)
- The Home Depot: Quikrete 80 lb Concrete Mix (bag yield and price)
- Estimators.us: Concrete Slab Cost in 2026, $6 to $12 per sq ft
- CalcShed: Concrete Slab Cost in 2026, per sq ft and by state
Frequently asked questions
How many bags of concrete for a 12x12 slab?
At 4 inches thick, 89 bags of 80 lb mix or 118 bags of 60 lb mix, including 10% extra for waste. That is 1.96 cubic yards of concrete.
How much does a 12x12 concrete slab cost?
Poured by a contractor, about $864 to $1,728 at 2026 rates of $6 to $12 per square foot for a 4-inch slab, including forming, pouring, and finishing. Doing it yourself, the concrete alone is $534 to $712 in bags or $304 to $522 delivered by truck, plus forms, gravel, and reinforcement.
How thick should a 12x12 slab be?
4 inches for a patio, a larger shed, or a carport pad. Go to 5 or 6 inches if vehicles will park on it, and use wire mesh or rebar in any slab that carries a load.
Is 4 inches enough for a carport on a 12 × 12 pad?
No. Anything a vehicle parks on should be 5 inches with #4 rebar on a 24-inch grid. Four inches is for patios and sheds. At this size the upgrade costs about half a cubic yard of concrete and one afternoon of tying rebar.
Does a 12 × 12 patio need an expansion joint where it meets the house?
Yes. A 1/2-inch fiber or foam expansion strip against the foundation lets the slab expand and settle without pushing on the wall. Skip it and the first hot summer or frost heave puts a crack along the house line.
Other common slab sizes
- 10 × 10 slab (a shed base, a small patio, or a hot tub pad)
- 16 × 12 slab (a standard backyard patio)
- 20 × 16 slab (a large patio or a workshop floor)
- 20 × 20 slab (a one-car garage floor or a driveway apron)
- 24 × 24 slab (a two-car garage floor)