Concrete for a 36×36 slab
16 cubic yards (792 × 80 lb bags)
for a 36×36 ft slab 4 inches thick: 432 cu ft. Bag counts include 10% extra; at 6 inches you need 24 yards.
A 36×36 foot slab covers 1296 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 432 cubic feet of concrete, or 16 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 17.75 yards, roughly $2,929 before delivery fees, against $5,148 for 792 bags of 80 lb mix.
Concrete for a 36×36 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 12 | 324 | 594 | 792 | 1188 |
| 4 in | 16 | 432 | 792 | 1056 | 1584 |
| 5 in | 20 | 540 | 990 | 1320 | 1980 |
| 6 in | 24 | 648 | 1188 | 1584 | 2376 |
| 8 in | 32 | 864 | 1584 | 2112 | 3168 |
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: 36 × 36 × 0.333 = 432 cu ft.
- Divide by 27 for cubic yards: 432 ÷ 27 = 16 cu yd.
- Add 10% and divide by the bag yield: 475.2 ÷ 0.6 = 792 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 16 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
- 32×36 slab
- 36×40 slab
- 30×36 slab
- 28×36 slab
- 26×36 slab
- 25×36 slab
- 24×36 slab
- 22×36 slab
- 36×50 slab
- 20×36 slab
- 18×36 slab
- 16×36 slab
Questions
- How many bags of concrete do I need for a 36×36 slab?
- At 4 inches thick, a 36×36 slab takes 792 bags of 80 lb concrete mix, 1056 bags of 60 lb mix or 1584 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 36×36 slab?
- 16 cubic yards at 4 inches thick, 20 at 5 inches and 24 at 6 inches, before adding extra for waste.
- How much does a 36×36 concrete slab cost?
- The concrete alone for a 4 inch 36×36 slab costs about $5,148 in 792 bags of 80 lb mix (at about $7 a bag) or about $2,929 for 17.75 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $7,776 to $15,552 for 1296 sq ft.
- How much does a 36×36 slab weigh?
- About 31.3 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).