Concrete for a 4×5 slab
0.25 cubic yards (13 × 80 lb bags)
for a 4×5 ft slab 4 inches thick: 6.7 cu ft. Bag counts include 10% extra; at 6 inches you need 0.37 yards.
A 4×5 foot slab covers 20 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 6.7 cubic feet of concrete, or 0.25 cubic yards. That is a small enough pour for bagged mix: 13 bags of 80 lb at about $85.
Concrete for a 4×5 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 0.19 | 5 | 10 | 13 | 19 |
| 4 in | 0.25 | 6.7 | 13 | 17 | 25 |
| 5 in | 0.31 | 8.3 | 16 | 21 | 31 |
| 6 in | 0.37 | 10 | 19 | 25 | 37 |
| 8 in | 0.49 | 13.3 | 25 | 33 | 49 |
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: 5 × 4 × 0.333 = 6.67 cu ft.
- Divide by 27 for cubic yards: 6.67 ÷ 27 = 0.247 cu yd.
- Add 10% and divide by the bag yield: 7.33 ÷ 0.6 = 13 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 0.25 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
- 4×4 slab
- 4×6 slab
- 3×5 slab
- 5×5 slab
- 3×4 slab
- 5×6 slab
- 4×8 slab
- 4×10 slab
- 5×8 slab
- 4×12 slab
- 5×10 slab
- 4×14 slab
Questions
- How many bags of concrete do I need for a 4×5 slab?
- At 4 inches thick, a 4×5 slab takes 13 bags of 80 lb concrete mix, 17 bags of 60 lb mix or 25 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 4×5 slab?
- 0.25 cubic yards at 4 inches thick, 0.31 at 5 inches and 0.37 at 6 inches, before adding extra for waste.
- How much does a 4×5 concrete slab cost?
- The concrete alone for a 4 inch 4×5 slab costs about $85 in 13 bags of 80 lb mix (at about $7 a bag) or about $83 for 0.5 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $120 to $240 for 20 sq ft.
- How much does a 4×5 slab weigh?
- About 0.5 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).