How Many Bags of Concrete for a 6×6 Slab?
A 6×6 foot slab — 36 square feet — at the standard 4-inch thickness needs 0.49 cubic yards of concrete: 22 bags of 80 lb or 30 bags of 60 lb, including 10% waste.
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Answer at a glance — 6×6 ft slab (36 sq ft)
| Thickness | Cu yards | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| 3.5" | 0.43 cu yd | 20 | 26 | 39 |
| 4" | 0.49 cu yd | 22 | 30 | 44 |
| 5" | 0.61 cu yd | 28 | 37 | 56 |
| 6" | 0.73 cu yd | 33 | 44 | 66 |
All counts include 10% waste, rounded up.
How we calculated it
- Area = 6 × 6 = 36 sq ft
- Volume = 36 × 4 ÷ 12 = 12 cu ft
- Cubic yards = 12 ÷ 27 = 0.44 cu yd
- With 10% waste = 0.49 cu yd
- 80 lb bags (45 per cu yd) → 22 bags
Bags vs. ready-mix
Your 6×6 slab needs 0.49 cubic yards — under 1 yard. Buying 22 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 6x6 slab?
A 6×6 ft slab (36 sq ft) at 4 inches thick needs 22 bags of 80 lb concrete or 30 bags of 60 lb. Includes a 10% waste factor.
How many cubic yards of concrete for a 6x6 slab?
At 4 inches thick: 0.49 cubic yards (with 10% waste). At 6 inches: 0.73 cu yd.
Should I use ready-mix or bags for a 6x6 slab?
At 0.49 cubic yards, bags are the practical choice. Mixing 22 bags (80 lb) by hand or with a rented mixer is manageable.
How thick should a 6x6 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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