Concrete for a 15×40 slab
7.41 cubic yards (367 × 80 lb bags)
for a 15×40 ft slab 4 inches thick: 200 cu ft. Bag counts include 10% extra; at 6 inches you need 11.11 yards.
A 15×40 foot slab covers 600 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 200 cubic feet of concrete, or 7.41 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 8.25 yards, roughly $1,361 before delivery fees, against $2,386 for 367 bags of 80 lb mix.
Concrete for a 15×40 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 5.56 | 150 | 275 | 367 | 550 |
| 4 in | 7.41 | 200 | 367 | 489 | 734 |
| 5 in | 9.26 | 250 | 459 | 612 | 917 |
| 6 in | 11.11 | 300 | 550 | 734 | 1100 |
| 8 in | 14.81 | 400 | 734 | 978 | 1467 |
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 × 15 × 0.333 = 200 cu ft.
- Divide by 27 for cubic yards: 200 ÷ 27 = 7.407 cu yd.
- Add 10% and divide by the bag yield: 220 ÷ 0.6 = 367 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 7.41 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
- 14×40 slab
- 16×40 slab
- 15×36 slab
- 12×40 slab
- 15×32 slab
- 18×40 slab
- 15×30 slab
- 15×50 slab
- 15×28 slab
- 10×40 slab
- 20×40 slab
- 15×26 slab
Questions
- How many bags of concrete do I need for a 15×40 slab?
- At 4 inches thick, a 15×40 slab takes 367 bags of 80 lb concrete mix, 489 bags of 60 lb mix or 734 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 15×40 slab?
- 7.41 cubic yards at 4 inches thick, 9.26 at 5 inches and 11.11 at 6 inches, before adding extra for waste.
- How much does a 15×40 concrete slab cost?
- The concrete alone for a 4 inch 15×40 slab costs about $2,386 in 367 bags of 80 lb mix (at about $7 a bag) or about $1,361 for 8.25 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $3,600 to $7,200 for 600 sq ft.
- How much does a 15×40 slab weigh?
- About 14.5 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).