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.
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.
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)