Concrete for a 3×5 slab
0.19 cubic yards (10 × 80 lb bags)
for a 3×5 ft slab 4 inches thick: 5 cu ft. Bag counts include 10% extra; at 6 inches you need 0.28 yards.
A 3×5 foot slab covers 15 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 5 cubic feet of concrete, or 0.19 cubic yards. That is a small enough pour for bagged mix: 10 bags of 80 lb at about $65.
Concrete for a 3×5 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 0.14 | 3.8 | 7 | 10 | 14 |
| 4 in | 0.19 | 5 | 10 | 13 | 19 |
| 5 in | 0.23 | 6.3 | 12 | 16 | 23 |
| 6 in | 0.28 | 7.5 | 14 | 19 | 28 |
| 8 in | 0.37 | 10 | 19 | 25 | 37 |
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 × 3 × 0.333 = 5 cu ft.
- Divide by 27 for cubic yards: 5 ÷ 27 = 0.185 cu yd.
- Add 10% and divide by the bag yield: 5.5 ÷ 0.6 = 10 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 0.19 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
- 3×4 slab
- 3×6 slab
- 4×5 slab
- 3×3 slab
- 3×8 slab
- 5×5 slab
- 3×10 slab
- 5×6 slab
- 3×12 slab
- 5×8 slab
- 3×14 slab
- 3×15 slab
Questions
- How many bags of concrete do I need for a 3×5 slab?
- At 4 inches thick, a 3×5 slab takes 10 bags of 80 lb concrete mix, 13 bags of 60 lb mix or 19 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 3×5 slab?
- 0.19 cubic yards at 4 inches thick, 0.23 at 5 inches and 0.28 at 6 inches, before adding extra for waste.
- How much does a 3×5 concrete slab cost?
- The concrete alone for a 4 inch 3×5 slab costs about $65 in 10 bags of 80 lb mix (at about $7 a bag) or about $41 for 0.25 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $90 to $180 for 15 sq ft.
- How much does a 3×5 slab weigh?
- About 0.4 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).