Concrete
How many yards of concrete for a 30×30 slab?
Quick Answer
A 30×30 foot slab at 4 inches thick requires approximately 11.1 cubic yards of concrete. At 6 inches thick (for a garage or heavy-use area), you need 16.7 cubic yards. Add 5–10% for waste and uneven subgrade, so order 12–13 yards at 4" or 17–18 yards at 6".
Quick Reference Table
| Thickness | Concrete for 30×30 slab |
|---|---|
| 4 inches | 11.1 yd³ (+10% = 12.2 yd³) |
| 5 inches | 13.9 yd³ (+10% = 15.3 yd³) |
| 6 inches | 16.7 yd³ (+10% = 18.3 yd³) |
How to Calculate It Yourself
- 1
Calculate volume: 30 × 30 × (4 ÷ 12) = 900 × 0.333 = 300 cubic feet.
- 2
Convert to cubic yards: 300 ÷ 27 = 11.11 yd³.
- 3
Add 10% for waste: 11.11 × 1.10 = 12.2 yd³.
- 4
A 30×30 slab requires 2 full concrete truck loads (typically 8–10 yd per load).
Pro Tip
For a garage floor (30×30), use 6-inch thickness with rebar on 18" centers and 4,000 PSI concrete. This supports vehicle traffic for decades without cracking.
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