Concrete for a 18×22 slab
4.89 cubic yards (242 × 80 lb bags)
for a 18×22 ft slab 4 inches thick: 132 cu ft. Bag counts include 10% extra; at 6 inches you need 7.33 yards.
A 18×22 foot slab covers 396 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 132 cubic feet of concrete, or 4.89 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 5.5 yards, roughly $908 before delivery fees, against $1,573 for 242 bags of 80 lb mix.
Concrete for a 18×22 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 3.67 | 99 | 182 | 242 | 363 |
| 4 in | 4.89 | 132 | 242 | 323 | 484 |
| 5 in | 6.11 | 165 | 303 | 404 | 605 |
| 6 in | 7.33 | 198 | 363 | 484 | 726 |
| 8 in | 9.78 | 264 | 484 | 646 | 968 |
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: 22 × 18 × 0.333 = 132 cu ft.
- Divide by 27 for cubic yards: 132 ÷ 27 = 4.889 cu yd.
- Add 10% and divide by the bag yield: 145.2 ÷ 0.6 = 242 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 4.89 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
- 18×20 slab
- 18×24 slab
- 16×22 slab
- 20×22 slab
- 18×25 slab
- 15×22 slab
- 18×18 slab
- 18×26 slab
- 14×22 slab
- 22×22 slab
- 16×18 slab
- 18×28 slab
Questions
- How many bags of concrete do I need for a 18×22 slab?
- At 4 inches thick, a 18×22 slab takes 242 bags of 80 lb concrete mix, 323 bags of 60 lb mix or 484 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 18×22 slab?
- 4.89 cubic yards at 4 inches thick, 6.11 at 5 inches and 7.33 at 6 inches, before adding extra for waste.
- How much does a 18×22 concrete slab cost?
- The concrete alone for a 4 inch 18×22 slab costs about $1,573 in 242 bags of 80 lb mix (at about $7 a bag) or about $908 for 5.5 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $2,376 to $4,752 for 396 sq ft.
- How much does a 18×22 slab weigh?
- About 9.6 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).