Concrete for a 36×40 slab
17.78 cubic yards (880 × 80 lb bags)
for a 36×40 ft slab 4 inches thick: 480 cu ft. Bag counts include 10% extra; at 6 inches you need 26.67 yards.
A 36×40 foot slab covers 1440 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 480 cubic feet of concrete, or 17.78 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 19.75 yards, roughly $3,259 before delivery fees, against $5,720 for 880 bags of 80 lb mix.
Concrete for a 36×40 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 13.33 | 360 | 660 | 880 | 1320 |
| 4 in | 17.78 | 480 | 880 | 1174 | 1760 |
| 5 in | 22.22 | 600 | 1100 | 1467 | 2200 |
| 6 in | 26.67 | 720 | 1320 | 1760 | 2640 |
| 8 in | 35.56 | 960 | 1760 | 2347 | 3520 |
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: 40 × 36 × 0.333 = 480 cu ft.
- Divide by 27 for cubic yards: 480 ÷ 27 = 17.778 cu yd.
- Add 10% and divide by the bag yield: 528 ÷ 0.6 = 880 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 17.78 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
- 36×36 slab
- 32×40 slab
- 40×40 slab
- 30×40 slab
- 32×36 slab
- 28×40 slab
- 30×36 slab
- 36×50 slab
- 26×40 slab
- 28×36 slab
- 25×40 slab
- 24×40 slab
Questions
- How many bags of concrete do I need for a 36×40 slab?
- At 4 inches thick, a 36×40 slab takes 880 bags of 80 lb concrete mix, 1174 bags of 60 lb mix or 1760 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 36×40 slab?
- 17.78 cubic yards at 4 inches thick, 22.22 at 5 inches and 26.67 at 6 inches, before adding extra for waste.
- How much does a 36×40 concrete slab cost?
- The concrete alone for a 4 inch 36×40 slab costs about $5,720 in 880 bags of 80 lb mix (at about $7 a bag) or about $3,259 for 19.75 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $8,640 to $17,280 for 1440 sq ft.
- How much does a 36×40 slab weigh?
- About 34.8 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).