Concrete for a 18×24 slab
5.33 cubic yards (264 × 80 lb bags)
for a 18×24 ft slab 4 inches thick: 144 cu ft. Bag counts include 10% extra; at 6 inches you need 8 yards.
A 18×24 foot slab covers 432 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 144 cubic feet of concrete, or 5.33 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 6 yards, roughly $990 before delivery fees, against $1,716 for 264 bags of 80 lb mix.
Concrete for a 18×24 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 4 | 108 | 198 | 264 | 396 |
| 4 in | 5.33 | 144 | 264 | 352 | 528 |
| 5 in | 6.67 | 180 | 330 | 440 | 660 |
| 6 in | 8 | 216 | 396 | 528 | 792 |
| 8 in | 10.67 | 288 | 528 | 704 | 1056 |
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: 24 × 18 × 0.333 = 144 cu ft.
- Divide by 27 for cubic yards: 144 ÷ 27 = 5.333 cu yd.
- Add 10% and divide by the bag yield: 158.4 ÷ 0.6 = 264 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 5.33 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
- 18×25 slab
- 18×22 slab
- 18×26 slab
- 16×24 slab
- 20×24 slab
- 15×24 slab
- 18×20 slab
- 18×28 slab
- 14×24 slab
- 22×24 slab
- 18×18 slab
- 18×30 slab
Questions
- How many bags of concrete do I need for a 18×24 slab?
- At 4 inches thick, a 18×24 slab takes 264 bags of 80 lb concrete mix, 352 bags of 60 lb mix or 528 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 18×24 slab?
- 5.33 cubic yards at 4 inches thick, 6.67 at 5 inches and 8 at 6 inches, before adding extra for waste.
- How much does a 18×24 concrete slab cost?
- The concrete alone for a 4 inch 18×24 slab costs about $1,716 in 264 bags of 80 lb mix (at about $7 a bag) or about $990 for 6 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $2,592 to $5,184 for 432 sq ft.
- How much does a 18×24 slab weigh?
- About 10.4 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).