Concrete for a 28×28 slab
9.68 cubic yards (480 × 80 lb bags)
for a 28×28 ft slab 4 inches thick: 261.3 cu ft. Bag counts include 10% extra; at 6 inches you need 14.52 yards.
A 28×28 foot slab covers 784 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 261.3 cubic feet of concrete, or 9.68 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 10.75 yards, roughly $1,774 before delivery fees, against $3,120 for 480 bags of 80 lb mix.
Concrete for a 28×28 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 7.26 | 196 | 360 | 480 | 719 |
| 4 in | 9.68 | 261.3 | 480 | 639 | 959 |
| 5 in | 12.1 | 326.7 | 599 | 799 | 1198 |
| 6 in | 14.52 | 392 | 719 | 959 | 1438 |
| 8 in | 19.36 | 522.7 | 959 | 1278 | 1917 |
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 × 28 × 0.333 = 261.33 cu ft.
- Divide by 27 for cubic yards: 261.33 ÷ 27 = 9.679 cu yd.
- Add 10% and divide by the bag yield: 287.47 ÷ 0.6 = 480 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 9.68 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
- 26×28 slab
- 28×30 slab
- 25×28 slab
- 24×28 slab
- 28×32 slab
- 22×28 slab
- 20×28 slab
- 28×36 slab
- 18×28 slab
- 16×28 slab
- 28×40 slab
- 15×28 slab
Questions
- How many bags of concrete do I need for a 28×28 slab?
- At 4 inches thick, a 28×28 slab takes 480 bags of 80 lb concrete mix, 639 bags of 60 lb mix or 959 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 28×28 slab?
- 9.68 cubic yards at 4 inches thick, 12.1 at 5 inches and 14.52 at 6 inches, before adding extra for waste.
- How much does a 28×28 concrete slab cost?
- The concrete alone for a 4 inch 28×28 slab costs about $3,120 in 480 bags of 80 lb mix (at about $7 a bag) or about $1,774 for 10.75 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $4,704 to $9,408 for 784 sq ft.
- How much does a 28×28 slab weigh?
- About 18.9 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).