Concrete for a 3×50 slab
1.85 cubic yards (92 × 80 lb bags)
for a 3×50 ft slab 4 inches thick: 50 cu ft. Bag counts include 10% extra; at 6 inches you need 2.78 yards.
A 3×50 foot slab covers 150 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 50 cubic feet of concrete, or 1.85 cubic yards. At this size you can mix 92 bags of 80 lb (about $598 and a long day of mixing) or order 2.25 yards of ready-mix (about $371, plus the short-load fee most suppliers charge under 3 to 4 yards).
Concrete for a 3×50 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 1.39 | 37.5 | 69 | 92 | 138 |
| 4 in | 1.85 | 50 | 92 | 123 | 184 |
| 5 in | 2.31 | 62.5 | 115 | 153 | 230 |
| 6 in | 2.78 | 75 | 138 | 184 | 275 |
| 8 in | 3.7 | 100 | 184 | 245 | 367 |
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 × 3 × 0.333 = 50 cu ft.
- Divide by 27 for cubic yards: 50 ÷ 27 = 1.852 cu yd.
- Add 10% and divide by the bag yield: 55 ÷ 0.6 = 92 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 1.85 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
- 3×40 slab
- 3×36 slab
- 4×50 slab
- 3×32 slab
- 3×30 slab
- 3×28 slab
- 3×26 slab
- 3×25 slab
- 3×24 slab
- 3×22 slab
- 3×20 slab
- 3×18 slab
Questions
- How many bags of concrete do I need for a 3×50 slab?
- At 4 inches thick, a 3×50 slab takes 92 bags of 80 lb concrete mix, 123 bags of 60 lb mix or 184 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 3×50 slab?
- 1.85 cubic yards at 4 inches thick, 2.31 at 5 inches and 2.78 at 6 inches, before adding extra for waste.
- How much does a 3×50 concrete slab cost?
- The concrete alone for a 4 inch 3×50 slab costs about $598 in 92 bags of 80 lb mix (at about $7 a bag) or about $371 for 2.25 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $900 to $1,800 for 150 sq ft.
- How much does a 3×50 slab weigh?
- About 3.6 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).