Concrete for a 3×3 slab
0.11 cubic yards (6 × 80 lb bags)
for a 3×3 ft slab 4 inches thick: 3 cu ft. Bag counts include 10% extra; at 6 inches you need 0.17 yards.
A 3×3 foot slab covers 9 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 3 cubic feet of concrete, or 0.11 cubic yards. That is a small enough pour for bagged mix: 6 bags of 80 lb at about $39.
Concrete for a 3×3 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 0.08 | 2.3 | 5 | 6 | 9 |
| 4 in | 0.11 | 3 | 6 | 8 | 11 |
| 5 in | 0.14 | 3.8 | 7 | 10 | 14 |
| 6 in | 0.17 | 4.5 | 9 | 11 | 17 |
| 8 in | 0.22 | 6 | 11 | 15 | 22 |
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: 3 × 3 × 0.333 = 3 cu ft.
- Divide by 27 for cubic yards: 3 ÷ 27 = 0.111 cu yd.
- Add 10% and divide by the bag yield: 3.3 ÷ 0.6 = 6 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 0.11 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
- 3×4 slab
- 3×5 slab
- 3×6 slab
- 3×8 slab
- 3×10 slab
- 3×12 slab
- 3×14 slab
- 3×15 slab
- 3×16 slab
- 3×18 slab
- 3×20 slab
- 3×22 slab
Questions
- How many bags of concrete do I need for a 3×3 slab?
- At 4 inches thick, a 3×3 slab takes 6 bags of 80 lb concrete mix, 8 bags of 60 lb mix or 11 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 3×3 slab?
- 0.11 cubic yards at 4 inches thick, 0.14 at 5 inches and 0.17 at 6 inches, before adding extra for waste.
- How much does a 3×3 concrete slab cost?
- The concrete alone for a 4 inch 3×3 slab costs about $39 in 6 bags of 80 lb mix (at about $7 a bag) or about $41 for 0.25 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $54 to $108 for 9 sq ft.
- How much does a 3×3 slab weigh?
- About 0.2 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).