Concrete for a 8×12 slab
1.19 cubic yards (59 × 80 lb bags)
for a 8×12 ft slab 4 inches thick: 32 cu ft. Bag counts include 10% extra; at 6 inches you need 1.78 yards.
A 8×12 foot slab covers 96 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 32 cubic feet of concrete, or 1.19 cubic yards. At this size you can mix 59 bags of 80 lb (about $384 and a long day of mixing) or order 1.5 yards of ready-mix (about $248, plus the short-load fee most suppliers charge under 3 to 4 yards).
Concrete for a 8×12 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 0.89 | 24 | 44 | 59 | 88 |
| 4 in | 1.19 | 32 | 59 | 79 | 118 |
| 5 in | 1.48 | 40 | 74 | 98 | 147 |
| 6 in | 1.78 | 48 | 88 | 118 | 176 |
| 8 in | 2.37 | 64 | 118 | 157 | 235 |
Bag counts include 10% extra for spillage and uneven ground. Cubic yards and cubic feet are the exact volume.
How it’s worked out
- Convert the thickness to feet: 4 in ÷ 12 = 0.333 ft.
- Multiply length × width × thickness: 12 × 8 × 0.333 = 32 cu ft.
- Divide by 27 for cubic yards: 32 ÷ 27 = 1.185 cu yd.
- Add 10% and divide by the bag yield: 35.2 ÷ 0.6 = 59 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 1.19 cubic yards. For driveways and anything that carries a vehicle, go to 5 or 6 inches and add rebar or wire mesh.
Change the numbers
Other slab sizes
- 8×10 slab
- 8×14 slab
- 6×12 slab
- 8×15 slab
- 10×12 slab
- 8×8 slab
- 8×16 slab
- 5×12 slab
- 4×12 slab
- 6×8 slab
- 8×18 slab
- 12×12 slab
Questions
- How many bags of concrete do I need for a 8×12 slab?
- At 4 inches thick, a 8×12 slab takes 59 bags of 80 lb concrete mix, 79 bags of 60 lb mix or 118 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 8×12 slab?
- 1.19 cubic yards at 4 inches thick, 1.48 at 5 inches and 1.78 at 6 inches, before adding extra for waste.
- How much does a 8×12 concrete slab cost?
- The concrete alone for a 4 inch 8×12 slab costs about $384 in 59 bags of 80 lb mix (at about $7 a bag) or about $248 for 1.5 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $576 to $1,152 for 96 sq ft.
- How much does a 8×12 slab weigh?
- About 2.3 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).