6×8 slab: concrete by thickness
| Thickness | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3.5″ | 14.00 | 0.52 | 24 | 32 |
| 4″ | 16.00 | 0.59 | 27 | 36 |
| 5″ | 20.00 | 0.74 | 34 | 45 |
| 6″ | 24.00 | 0.89 | 40 | 54 |
No waste included in the table.
Worked example
6 ft × 8 ft = 48 sq ft. At 4 inches: 48 × 4 ÷ 12 = 16.00 cu ft, or 0.59 cubic yards. With 10% extra that is 0.65 yd³, or 30 bags of 80 lb mix.
At this size, bagged mix is manageable by hand.
Assumes standard concrete mix bag yields: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft. Check the yield on your bag. 1 cubic yard = 27 cubic feet.
Frequently asked questions
How many bags of concrete for a 6×8 slab?
27 × 80 lb or 36 × 60 lb bags at 4 inches thick, before waste.
How many yards of concrete for a 6×8 slab?
0.59 cubic yards at 4 inches; 0.89 at 6 inches.