Concrete for a 28×30 slab
10.37 cubic yards (514 × 80 lb bags)
for a 28×30 ft slab 4 inches thick: 280 cu ft. Bag counts include 10% extra; at 6 inches you need 15.56 yards.
A 28×30 foot slab covers 840 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 280 cubic feet of concrete, or 10.37 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 11.5 yards, roughly $1,898 before delivery fees, against $3,341 for 514 bags of 80 lb mix.
Concrete for a 28×30 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 7.78 | 210 | 385 | 514 | 770 |
| 4 in | 10.37 | 280 | 514 | 685 | 1027 |
| 5 in | 12.96 | 350 | 642 | 856 | 1284 |
| 6 in | 15.56 | 420 | 770 | 1027 | 1540 |
| 8 in | 20.74 | 560 | 1027 | 1369 | 2054 |
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: 30 × 28 × 0.333 = 280 cu ft.
- Divide by 27 for cubic yards: 280 ÷ 27 = 10.37 cu yd.
- Add 10% and divide by the bag yield: 308 ÷ 0.6 = 514 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 10.37 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
- 28×28 slab
- 28×32 slab
- 26×30 slab
- 30×30 slab
- 25×30 slab
- 26×28 slab
- 24×30 slab
- 30×32 slab
- 25×28 slab
- 24×28 slab
- 28×36 slab
- 22×30 slab
Questions
- How many bags of concrete do I need for a 28×30 slab?
- At 4 inches thick, a 28×30 slab takes 514 bags of 80 lb concrete mix, 685 bags of 60 lb mix or 1027 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 28×30 slab?
- 10.37 cubic yards at 4 inches thick, 12.96 at 5 inches and 15.56 at 6 inches, before adding extra for waste.
- How much does a 28×30 concrete slab cost?
- The concrete alone for a 4 inch 28×30 slab costs about $3,341 in 514 bags of 80 lb mix (at about $7 a bag) or about $1,898 for 11.5 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $5,040 to $10,080 for 840 sq ft.
- How much does a 28×30 slab weigh?
- About 20.3 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).