How much concrete for a 12 x 24 slab?
Short answer
- A 12 x 24 ft slab is 288 square feet. At 4 inches thick it needs 3.56 cubic yards (96 cubic feet) of concrete.
- With 10% extra that's 3.91 cubic yards, so you'd order 4 cubic yards of ready-mix (plants sell in quarter-yard steps). By the bag it's 176 bags of 80 lb.
- It's typically a garage-sized pad or a large patio.
Concrete for a 12 x 24 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 | 3.56 | 176 | 235 | 352 | 7.4 to 7.9 tons |
| 5 in | 4.44 | 220 | 294 | 440 | 9.2 to 9.9 tons |
| 6 in | 5.33 | 264 | 352 | 528 | 11.1 to 11.9 tons |
Open this slab in the concrete calculator to change the size, thickness, waste or bag size.
How the math works
12 ft × 24 ft × 4 in ÷ 12 = 96 cubic feet. Divide by 27 to get 3.56 cubic yards. Add 10% and you have 105.6 cubic feet. An 80 lb bag of premixed concrete yields about 0.60 cubic feet, so 105.6 ÷ 0.60 rounds up to 176 bags.
Bags or ready-mix?
At 3.56 cubic yards, a 4 inch 12 x 24 slab means mixing 176 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 72 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 24 slab that's 120 cubic feet of loose gravel, about 4.44 cubic yards or 6.3 tons at 105 lb per cubic foot. The slab planner adds rebar or mesh and totals the cost with your local prices. For a garage floor, check your local code for the base it requires.
Other slab sizes
- 12 x 12 slab144 sq ft, typically a patio or a shed base.
- 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.
- 16 x 16 slab256 sq ft, typically a large patio.
- 20 x 20 slab400 sq ft, typically a two-car parking pad.
- 20 x 24 slab480 sq ft, typically a two-car garage floor.