Concrete for a 16×18 slab
3.56 cubic yards (176 × 80 lb bags)
for a 16×18 ft slab 4 inches thick: 96 cu ft. Bag counts include 10% extra; at 6 inches you need 5.33 yards.
A 16×18 foot slab covers 288 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 96 cubic feet of concrete, or 3.56 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 4 yards, roughly $660 before delivery fees, against $1,144 for 176 bags of 80 lb mix.
Concrete for a 16×18 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 2.67 | 72 | 132 | 176 | 264 |
| 4 in | 3.56 | 96 | 176 | 235 | 352 |
| 5 in | 4.44 | 120 | 220 | 294 | 440 |
| 6 in | 5.33 | 144 | 264 | 352 | 528 |
| 8 in | 7.11 | 192 | 352 | 470 | 704 |
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: 18 × 16 × 0.333 = 96 cu ft.
- Divide by 27 for cubic yards: 96 ÷ 27 = 3.556 cu yd.
- Add 10% and divide by the bag yield: 105.6 ÷ 0.6 = 176 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 3.56 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
- 15×18 slab
- 16×16 slab
- 16×20 slab
- 14×18 slab
- 18×18 slab
- 15×16 slab
- 14×16 slab
- 16×22 slab
- 12×18 slab
- 18×20 slab
- 12×16 slab
- 16×24 slab
Questions
- How many bags of concrete do I need for a 16×18 slab?
- At 4 inches thick, a 16×18 slab takes 176 bags of 80 lb concrete mix, 235 bags of 60 lb mix or 352 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 16×18 slab?
- 3.56 cubic yards at 4 inches thick, 4.44 at 5 inches and 5.33 at 6 inches, before adding extra for waste.
- How much does a 16×18 concrete slab cost?
- The concrete alone for a 4 inch 16×18 slab costs about $1,144 in 176 bags of 80 lb mix (at about $7 a bag) or about $660 for 4 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $1,728 to $3,456 for 288 sq ft.
- How much does a 16×18 slab weigh?
- About 7 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).