Concrete for a 28×36 slab
12.44 cubic yards (616 × 80 lb bags)
for a 28×36 ft slab 4 inches thick: 336 cu ft. Bag counts include 10% extra; at 6 inches you need 18.67 yards.
A 28×36 foot slab covers 1008 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 336 cubic feet of concrete, or 12.44 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 13.75 yards, roughly $2,269 before delivery fees, against $4,004 for 616 bags of 80 lb mix.
Concrete for a 28×36 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 9.33 | 252 | 462 | 616 | 924 |
| 4 in | 12.44 | 336 | 616 | 822 | 1232 |
| 5 in | 15.56 | 420 | 770 | 1027 | 1540 |
| 6 in | 18.67 | 504 | 924 | 1232 | 1848 |
| 8 in | 24.89 | 672 | 1232 | 1643 | 2464 |
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 × 28 × 0.333 = 336 cu ft.
- Divide by 27 for cubic yards: 336 ÷ 27 = 12.444 cu yd.
- Add 10% and divide by the bag yield: 369.6 ÷ 0.6 = 616 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 12.44 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
- 26×36 slab
- 30×36 slab
- 25×36 slab
- 28×32 slab
- 28×40 slab
- 24×36 slab
- 32×36 slab
- 28×30 slab
- 22×36 slab
- 28×28 slab
- 26×28 slab
- 20×36 slab
Questions
- How many bags of concrete do I need for a 28×36 slab?
- At 4 inches thick, a 28×36 slab takes 616 bags of 80 lb concrete mix, 822 bags of 60 lb mix or 1232 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 28×36 slab?
- 12.44 cubic yards at 4 inches thick, 15.56 at 5 inches and 18.67 at 6 inches, before adding extra for waste.
- How much does a 28×36 concrete slab cost?
- The concrete alone for a 4 inch 28×36 slab costs about $4,004 in 616 bags of 80 lb mix (at about $7 a bag) or about $2,269 for 13.75 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $6,048 to $12,096 for 1008 sq ft.
- How much does a 28×36 slab weigh?
- About 24.4 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).