Concrete for a 15×36 slab
6.67 cubic yards (330 × 80 lb bags)
for a 15×36 ft slab 4 inches thick: 180 cu ft. Bag counts include 10% extra; at 6 inches you need 10 yards.
A 15×36 foot slab covers 540 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 180 cubic feet of concrete, or 6.67 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 7.5 yards, roughly $1,238 before delivery fees, against $2,145 for 330 bags of 80 lb mix.
Concrete for a 15×36 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 5 | 135 | 248 | 330 | 495 |
| 4 in | 6.67 | 180 | 330 | 440 | 660 |
| 5 in | 8.33 | 225 | 413 | 550 | 825 |
| 6 in | 10 | 270 | 495 | 660 | 990 |
| 8 in | 13.33 | 360 | 660 | 880 | 1320 |
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 × 15 × 0.333 = 180 cu ft.
- Divide by 27 for cubic yards: 180 ÷ 27 = 6.667 cu yd.
- Add 10% and divide by the bag yield: 198 ÷ 0.6 = 330 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 6.67 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
- 14×36 slab
- 16×36 slab
- 15×32 slab
- 15×40 slab
- 15×30 slab
- 12×36 slab
- 18×36 slab
- 15×28 slab
- 15×26 slab
- 15×25 slab
- 10×36 slab
- 15×24 slab
Questions
- How many bags of concrete do I need for a 15×36 slab?
- At 4 inches thick, a 15×36 slab takes 330 bags of 80 lb concrete mix, 440 bags of 60 lb mix or 660 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 15×36 slab?
- 6.67 cubic yards at 4 inches thick, 8.33 at 5 inches and 10 at 6 inches, before adding extra for waste.
- How much does a 15×36 concrete slab cost?
- The concrete alone for a 4 inch 15×36 slab costs about $2,145 in 330 bags of 80 lb mix (at about $7 a bag) or about $1,238 for 7.5 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $3,240 to $6,480 for 540 sq ft.
- How much does a 15×36 slab weigh?
- About 13.1 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).