Concrete for a 3×8 slab
0.3 cubic yards (15 × 80 lb bags)
for a 3×8 ft slab 4 inches thick: 8 cu ft. Bag counts include 10% extra; at 6 inches you need 0.44 yards.
A 3×8 foot slab covers 24 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 8 cubic feet of concrete, or 0.3 cubic yards. That is a small enough pour for bagged mix: 15 bags of 80 lb at about $98.
Concrete for a 3×8 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 0.22 | 6 | 11 | 15 | 22 |
| 4 in | 0.3 | 8 | 15 | 20 | 30 |
| 5 in | 0.37 | 10 | 19 | 25 | 37 |
| 6 in | 0.44 | 12 | 22 | 30 | 44 |
| 8 in | 0.59 | 16 | 30 | 40 | 59 |
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: 8 × 3 × 0.333 = 8 cu ft.
- Divide by 27 for cubic yards: 8 ÷ 27 = 0.296 cu yd.
- Add 10% and divide by the bag yield: 8.8 ÷ 0.6 = 15 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 0.3 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
- 3×6 slab
- 3×10 slab
- 4×8 slab
- 3×5 slab
- 3×4 slab
- 3×12 slab
- 3×3 slab
- 5×8 slab
- 3×14 slab
- 3×15 slab
- 3×16 slab
- 6×8 slab
Questions
- How many bags of concrete do I need for a 3×8 slab?
- At 4 inches thick, a 3×8 slab takes 15 bags of 80 lb concrete mix, 20 bags of 60 lb mix or 30 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 3×8 slab?
- 0.3 cubic yards at 4 inches thick, 0.37 at 5 inches and 0.44 at 6 inches, before adding extra for waste.
- How much does a 3×8 concrete slab cost?
- The concrete alone for a 4 inch 3×8 slab costs about $98 in 15 bags of 80 lb mix (at about $7 a bag) or about $83 for 0.5 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $144 to $288 for 24 sq ft.
- How much does a 3×8 slab weigh?
- About 0.6 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).