How Many Bags of Concrete for a 8×8 Slab?
A 8×8 foot slab — 64 square feet — at the standard 4-inch thickness needs 0.87 cubic yards of concrete: 40 bags of 80 lb or 53 bags of 60 lb, including 10% waste.
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Answer at a glance — 8×8 ft slab (64 sq ft)
| Thickness | Cu yards | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| 3.5" | 0.76 cu yd | 35 | 46 | 69 |
| 4" | 0.87 cu yd | 40 | 53 | 79 |
| 5" | 1.09 cu yd | 49 | 66 | 98 |
| 6" | 1.3 cu yd | 59 | 79 | 118 |
All counts include 10% waste, rounded up.
How we calculated it
- Area = 8 × 8 = 64 sq ft
- Volume = 64 × 4 ÷ 12 = 21.33 cu ft
- Cubic yards = 21.33 ÷ 27 = 0.79 cu yd
- With 10% waste = 0.87 cu yd
- 80 lb bags (45 per cu yd) → 40 bags
Bags vs. ready-mix
Your 8×8 slab needs 0.87 cubic yards — under 1 yard. Buying 40 bags (80 lb) is the practical choice. A rented mixer makes the job easier for anything over 20 bags.
Thickness reference
| Use | Recommended thickness |
|---|---|
| Sidewalk, path | 4 inches |
| Patio, shed base | 4 inches |
| Driveway (cars) | 5 inches |
| Driveway (trucks/RVs) | 6 inches |
| Garage floor | 4–6 inches + rebar |
Use the Concrete Calculator to enter your exact dimensions and get a precise bag count and cost estimate.
Frequently Asked Questions
How many bags of concrete for a 8x8 slab?
A 8×8 ft slab (64 sq ft) at 4 inches thick needs 40 bags of 80 lb concrete or 53 bags of 60 lb. Includes a 10% waste factor.
How many cubic yards of concrete for a 8x8 slab?
At 4 inches thick: 0.87 cubic yards (with 10% waste). At 6 inches: 1.3 cu yd.
Should I use ready-mix or bags for a 8x8 slab?
At 0.87 cubic yards, bags are the practical choice. Mixing 40 bags (80 lb) by hand or with a rented mixer is manageable.
How thick should a 8x8 concrete slab be?
For a patio or shed base: 4 inches. For a driveway with passenger cars: 5 inches. For heavy vehicles: 6 inches. Garages typically use 4–6 inches with wire mesh or rebar.
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