How much concrete for a 12 x 12 slab?
Short answer
- A 12 x 12 ft slab is 144 square feet. At 4 inches thick it needs 1.78 cubic yards (48 cubic feet) of concrete.
- With 10% extra that's 1.96 cubic yards, so you'd order 2 cubic yards of ready-mix (plants sell in quarter-yard steps). By the bag it's 88 bags of 80 lb.
- It's typically a patio or a shed base.
Concrete for a 12 x 12 slab at 4, 5 and 6 inches
Bag counts include 10% extra for uneven ground and spillage. Cubic yards are shown without extra so you can compare quotes.
| Thickness | Cubic yards | 80 lb bags | 60 lb bags | 40 lb bags | Weight with extra |
|---|---|---|---|---|---|
| 4 in | 1.78 | 88 | 118 | 176 | 3.7 to 4 tons |
| 5 in | 2.22 | 110 | 147 | 220 | 4.6 to 5 tons |
| 6 in | 2.67 | 132 | 176 | 264 | 5.5 to 5.9 tons |
Open this slab in the concrete calculator to change the size, thickness, waste or bag size.
How the math works
12 ft × 12 ft × 4 in ÷ 12 = 48 cubic feet. Divide by 27 to get 1.78 cubic yards. Add 10% and you have 52.8 cubic feet. An 80 lb bag of premixed concrete yields about 0.60 cubic feet, so 52.8 ÷ 0.60 rounds up to 88 bags.
Bags or ready-mix?
At 1.78 cubic yards, a 4 inch 12 x 12 slab means mixing 88 bags by hand. Price a ready-mix load too, and ask about the minimum order and short-load fees before you decide.
Forms and gravel base
The slab's edge is 48 feet, so that's how much form board you need around it, plus stakes. Under it, Quikrete's patio steps call for 5 inches of loose gravel tamped down to 4. For a 12 x 12 slab that's 60 cubic feet of loose gravel, about 2.22 cubic yards or 3.2 tons at 105 lb per cubic foot. The slab planner adds rebar or mesh and totals the cost with your local prices.
Other slab sizes
- 10 x 10 slab100 sq ft, typically a small patio or a shed base.
- 10 x 12 slab120 sq ft, typically a patio or a 10 x 12 shed base.
- 10 x 20 slab200 sq ft, typically a long patio or a carport strip.
- 12 x 16 slab192 sq ft, typically a larger shed or a patio.
- 12 x 20 slab240 sq ft, typically a patio or a single parking pad.
- 12 x 24 slab288 sq ft, typically a garage-sized pad or a large patio.