Concrete for a 30×30 slab
11.11 cubic yards (550 × 80 lb bags)
for a 30×30 ft slab 4 inches thick: 300 cu ft. Bag counts include 10% extra; at 6 inches you need 16.67 yards.
A 30×30 foot slab covers 900 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 300 cubic feet of concrete, or 11.11 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 12.25 yards, roughly $2,021 before delivery fees, against $3,575 for 550 bags of 80 lb mix.
Concrete for a 30×30 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 8.33 | 225 | 413 | 550 | 825 |
| 4 in | 11.11 | 300 | 550 | 734 | 1100 |
| 5 in | 13.89 | 375 | 688 | 917 | 1375 |
| 6 in | 16.67 | 450 | 825 | 1100 | 1650 |
| 8 in | 22.22 | 600 | 1100 | 1467 | 2200 |
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 × 30 × 0.333 = 300 cu ft.
- Divide by 27 for cubic yards: 300 ÷ 27 = 11.111 cu yd.
- Add 10% and divide by the bag yield: 330 ÷ 0.6 = 550 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 11.11 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
- 28×30 slab
- 30×32 slab
- 26×30 slab
- 25×30 slab
- 24×30 slab
- 30×36 slab
- 22×30 slab
- 20×30 slab
- 30×40 slab
- 18×30 slab
- 16×30 slab
- 15×30 slab
Questions
- How many bags of concrete do I need for a 30×30 slab?
- At 4 inches thick, a 30×30 slab takes 550 bags of 80 lb concrete mix, 734 bags of 60 lb mix or 1100 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 30×30 slab?
- 11.11 cubic yards at 4 inches thick, 13.89 at 5 inches and 16.67 at 6 inches, before adding extra for waste.
- How much does a 30×30 concrete slab cost?
- The concrete alone for a 4 inch 30×30 slab costs about $3,575 in 550 bags of 80 lb mix (at about $7 a bag) or about $2,021 for 12.25 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $5,400 to $10,800 for 900 sq ft.
- How much does a 30×30 slab weigh?
- About 21.8 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).