Concrete for a 8×28 slab
2.77 cubic yards (137 × 80 lb bags)
for a 8×28 ft slab 4 inches thick: 74.7 cu ft. Bag counts include 10% extra; at 6 inches you need 4.15 yards.
A 8×28 foot slab covers 224 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 74.7 cubic feet of concrete, or 2.77 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 3.25 yards, roughly $536 before delivery fees, against $891 for 137 bags of 80 lb mix.
Concrete for a 8×28 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 2.07 | 56 | 103 | 137 | 206 |
| 4 in | 2.77 | 74.7 | 137 | 183 | 274 |
| 5 in | 3.46 | 93.3 | 172 | 229 | 343 |
| 6 in | 4.15 | 112 | 206 | 274 | 411 |
| 8 in | 5.53 | 149.3 | 274 | 366 | 548 |
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: 28 × 8 × 0.333 = 74.67 cu ft.
- Divide by 27 for cubic yards: 74.67 ÷ 27 = 2.765 cu yd.
- Add 10% and divide by the bag yield: 82.13 ÷ 0.6 = 137 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 2.77 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
- 8×26 slab
- 8×30 slab
- 8×25 slab
- 8×24 slab
- 8×32 slab
- 8×22 slab
- 6×28 slab
- 10×28 slab
- 8×20 slab
- 8×36 slab
- 8×18 slab
- 5×28 slab
Questions
- How many bags of concrete do I need for a 8×28 slab?
- At 4 inches thick, a 8×28 slab takes 137 bags of 80 lb concrete mix, 183 bags of 60 lb mix or 274 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 8×28 slab?
- 2.77 cubic yards at 4 inches thick, 3.46 at 5 inches and 4.15 at 6 inches, before adding extra for waste.
- How much does a 8×28 concrete slab cost?
- The concrete alone for a 4 inch 8×28 slab costs about $891 in 137 bags of 80 lb mix (at about $7 a bag) or about $536 for 3.25 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $1,344 to $2,688 for 224 sq ft.
- How much does a 8×28 slab weigh?
- About 5.4 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).