8×8 slab: concrete by thickness
| Thickness | Cu ft | Cu yd | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3.5″ | 18.67 | 0.69 | 32 | 42 |
| 4″ | 21.33 | 0.79 | 36 | 48 |
| 5″ | 26.67 | 0.99 | 45 | 60 |
| 6″ | 32.00 | 1.19 | 54 | 72 |
No waste included in the table.
Worked example
8 ft × 8 ft = 64 sq ft. At 4 inches: 64 × 4 ÷ 12 = 21.33 cu ft, or 0.79 cubic yards. With 10% extra that is 0.87 yd³, or 40 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 8×8 slab?
36 × 80 lb or 48 × 60 lb bags at 4 inches thick, before waste.
How many yards of concrete for a 8×8 slab?
0.79 cubic yards at 4 inches; 1.19 at 6 inches.