Concrete for a 3×30 slab
1.11 cubic yards (55 × 80 lb bags)
for a 3×30 ft slab 4 inches thick: 30 cu ft. Bag counts include 10% extra; at 6 inches you need 1.67 yards.
A 3×30 foot slab covers 90 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 30 cubic feet of concrete, or 1.11 cubic yards. At this size you can mix 55 bags of 80 lb (about $358 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 3×30 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 0.83 | 22.5 | 42 | 55 | 83 |
| 4 in | 1.11 | 30 | 55 | 74 | 110 |
| 5 in | 1.39 | 37.5 | 69 | 92 | 138 |
| 6 in | 1.67 | 45 | 83 | 110 | 165 |
| 8 in | 2.22 | 60 | 110 | 147 | 220 |
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 × 3 × 0.333 = 30 cu ft.
- Divide by 27 for cubic yards: 30 ÷ 27 = 1.111 cu yd.
- Add 10% and divide by the bag yield: 33 ÷ 0.6 = 55 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 1.11 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
- 3×28 slab
- 3×32 slab
- 3×26 slab
- 3×25 slab
- 3×24 slab
- 3×36 slab
- 3×22 slab
- 3×20 slab
- 3×40 slab
- 4×30 slab
- 3×18 slab
- 3×16 slab
Questions
- How many bags of concrete do I need for a 3×30 slab?
- At 4 inches thick, a 3×30 slab takes 55 bags of 80 lb concrete mix, 74 bags of 60 lb mix or 110 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 3×30 slab?
- 1.11 cubic yards at 4 inches thick, 1.39 at 5 inches and 1.67 at 6 inches, before adding extra for waste.
- How much does a 3×30 concrete slab cost?
- The concrete alone for a 4 inch 3×30 slab costs about $358 in 55 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 $540 to $1,080 for 90 sq ft.
- How much does a 3×30 slab weigh?
- About 2.2 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).