Concrete for a 40×50 slab
24.69 cubic yards (1223 × 80 lb bags)
for a 40×50 ft slab 4 inches thick: 666.7 cu ft. Bag counts include 10% extra; at 6 inches you need 37.04 yards.
A 40×50 foot slab covers 2000 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 666.7 cubic feet of concrete, or 24.69 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 27.25 yards, roughly $4,496 before delivery fees, against $7,950 for 1223 bags of 80 lb mix.
Concrete for a 40×50 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 18.52 | 500 | 917 | 1223 | 1834 |
| 4 in | 24.69 | 666.7 | 1223 | 1630 | 2445 |
| 5 in | 30.86 | 833.3 | 1528 | 2038 | 3056 |
| 6 in | 37.04 | 1,000 | 1834 | 2445 | 3667 |
| 8 in | 49.38 | 1,333.3 | 2445 | 3260 | 4889 |
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: 50 × 40 × 0.333 = 666.67 cu ft.
- Divide by 27 for cubic yards: 666.67 ÷ 27 = 24.691 cu yd.
- Add 10% and divide by the bag yield: 733.33 ÷ 0.6 = 1223 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 24.69 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
- 36×50 slab
- 32×50 slab
- 40×40 slab
- 30×50 slab
- 50×50 slab
- 36×40 slab
- 28×50 slab
- 26×50 slab
- 32×40 slab
- 25×50 slab
- 24×50 slab
- 30×40 slab
Questions
- How many bags of concrete do I need for a 40×50 slab?
- At 4 inches thick, a 40×50 slab takes 1223 bags of 80 lb concrete mix, 1630 bags of 60 lb mix or 2445 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 40×50 slab?
- 24.69 cubic yards at 4 inches thick, 30.86 at 5 inches and 37.04 at 6 inches, before adding extra for waste.
- How much does a 40×50 concrete slab cost?
- The concrete alone for a 4 inch 40×50 slab costs about $7,950 in 1223 bags of 80 lb mix (at about $7 a bag) or about $4,496 for 27.25 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $12,000 to $24,000 for 2000 sq ft.
- How much does a 40×50 slab weigh?
- About 48.3 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).