Concrete for a 15×28 slab
5.19 cubic yards (257 × 80 lb bags)
for a 15×28 ft slab 4 inches thick: 140 cu ft. Bag counts include 10% extra; at 6 inches you need 7.78 yards.
A 15×28 foot slab covers 420 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 140 cubic feet of concrete, or 5.19 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 5.75 yards, roughly $949 before delivery fees, against $1,671 for 257 bags of 80 lb mix.
Concrete for a 15×28 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 3.89 | 105 | 193 | 257 | 385 |
| 4 in | 5.19 | 140 | 257 | 343 | 514 |
| 5 in | 6.48 | 175 | 321 | 428 | 642 |
| 6 in | 7.78 | 210 | 385 | 514 | 770 |
| 8 in | 10.37 | 280 | 514 | 685 | 1027 |
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 × 15 × 0.333 = 140 cu ft.
- Divide by 27 for cubic yards: 140 ÷ 27 = 5.185 cu yd.
- Add 10% and divide by the bag yield: 154 ÷ 0.6 = 257 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 5.19 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
- 14×28 slab
- 16×28 slab
- 15×26 slab
- 15×30 slab
- 15×25 slab
- 15×24 slab
- 15×32 slab
- 12×28 slab
- 18×28 slab
- 15×22 slab
- 15×20 slab
- 15×36 slab
Questions
- How many bags of concrete do I need for a 15×28 slab?
- At 4 inches thick, a 15×28 slab takes 257 bags of 80 lb concrete mix, 343 bags of 60 lb mix or 514 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 15×28 slab?
- 5.19 cubic yards at 4 inches thick, 6.48 at 5 inches and 7.78 at 6 inches, before adding extra for waste.
- How much does a 15×28 concrete slab cost?
- The concrete alone for a 4 inch 15×28 slab costs about $1,671 in 257 bags of 80 lb mix (at about $7 a bag) or about $949 for 5.75 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $2,520 to $5,040 for 420 sq ft.
- How much does a 15×28 slab weigh?
- About 10.2 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).