Concrete for a 3×28 slab
1.04 cubic yards (52 × 80 lb bags)
for a 3×28 ft slab 4 inches thick: 28 cu ft. Bag counts include 10% extra; at 6 inches you need 1.56 yards.
A 3×28 foot slab covers 84 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 28 cubic feet of concrete, or 1.04 cubic yards. At this size you can mix 52 bags of 80 lb (about $338 and a long day of mixing) or order 1.25 yards of ready-mix (about $206, plus the short-load fee most suppliers charge under 3 to 4 yards).
Concrete for a 3×28 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 0.78 | 21 | 39 | 52 | 77 |
| 4 in | 1.04 | 28 | 52 | 69 | 103 |
| 5 in | 1.3 | 35 | 65 | 86 | 129 |
| 6 in | 1.56 | 42 | 77 | 103 | 154 |
| 8 in | 2.07 | 56 | 103 | 137 | 206 |
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 × 3 × 0.333 = 28 cu ft.
- Divide by 27 for cubic yards: 28 ÷ 27 = 1.037 cu yd.
- Add 10% and divide by the bag yield: 30.8 ÷ 0.6 = 52 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 1.04 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
- 3×26 slab
- 3×30 slab
- 3×25 slab
- 3×24 slab
- 3×32 slab
- 3×22 slab
- 3×20 slab
- 3×36 slab
- 4×28 slab
- 3×18 slab
- 3×16 slab
- 3×40 slab
Questions
- How many bags of concrete do I need for a 3×28 slab?
- At 4 inches thick, a 3×28 slab takes 52 bags of 80 lb concrete mix, 69 bags of 60 lb mix or 103 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 3×28 slab?
- 1.04 cubic yards at 4 inches thick, 1.3 at 5 inches and 1.56 at 6 inches, before adding extra for waste.
- How much does a 3×28 concrete slab cost?
- The concrete alone for a 4 inch 3×28 slab costs about $338 in 52 bags of 80 lb mix (at about $7 a bag) or about $206 for 1.25 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $504 to $1,008 for 84 sq ft.
- How much does a 3×28 slab weigh?
- About 2 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).