Concrete for a 30×36 slab
13.33 cubic yards (660 × 80 lb bags)
for a 30×36 ft slab 4 inches thick: 360 cu ft. Bag counts include 10% extra; at 6 inches you need 20 yards.
A 30×36 foot slab covers 1080 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 360 cubic feet of concrete, or 13.33 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 14.75 yards, roughly $2,434 before delivery fees, against $4,290 for 660 bags of 80 lb mix.
Concrete for a 30×36 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 10 | 270 | 495 | 660 | 990 |
| 4 in | 13.33 | 360 | 660 | 880 | 1320 |
| 5 in | 16.67 | 450 | 825 | 1100 | 1650 |
| 6 in | 20 | 540 | 990 | 1320 | 1980 |
| 8 in | 26.67 | 720 | 1320 | 1760 | 2640 |
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 × 30 × 0.333 = 360 cu ft.
- Divide by 27 for cubic yards: 360 ÷ 27 = 13.333 cu yd.
- Add 10% and divide by the bag yield: 396 ÷ 0.6 = 660 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 13.33 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
- 28×36 slab
- 32×36 slab
- 30×32 slab
- 30×40 slab
- 26×36 slab
- 25×36 slab
- 30×30 slab
- 24×36 slab
- 36×36 slab
- 28×30 slab
- 22×36 slab
- 26×30 slab
Questions
- How many bags of concrete do I need for a 30×36 slab?
- At 4 inches thick, a 30×36 slab takes 660 bags of 80 lb concrete mix, 880 bags of 60 lb mix or 1320 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 30×36 slab?
- 13.33 cubic yards at 4 inches thick, 16.67 at 5 inches and 20 at 6 inches, before adding extra for waste.
- How much does a 30×36 concrete slab cost?
- The concrete alone for a 4 inch 30×36 slab costs about $4,290 in 660 bags of 80 lb mix (at about $7 a bag) or about $2,434 for 14.75 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $6,480 to $12,960 for 1080 sq ft.
- How much does a 30×36 slab weigh?
- About 26.1 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).