Concrete for a 20x30 Slab
Order 8.15 yd with 10% waste — or 334 × 80 lb bags / 445 × 60 lb bags.
By thickness
| Thickness | Cubic yards | +10% waste | 80 lb bags | Typical use |
|---|---|---|---|---|
| 4" | 7.41 | 8.15 | 334 | Patio, shed pad, walkway |
| 5" | 9.26 | 10.19 | 417 | Light vehicle traffic |
| 6" | 11.11 | 12.22 | 500 | Driveway, garage |
Bags or the truck?
For this 600 sq ft slab at 4": bags ≈ $2,171 (334 × 80 lb — that's 26,720 lb of mixing) vs ready-mix ≈ $1,148 delivered. The truck wins here. Prices are national ballparks — your local quote rules.
Adjust the numbers
Common questions
How much concrete do I need for a 20x30 slab?
A 20x30 slab at the standard 4-inch thickness needs 7.41 cubic yards of concrete — order 8.15 yards with a 10% waste margin. At 6 inches it needs 11.11 yards.
How many bags of concrete for a 20x30 slab?
At 4 inches thick: 334 bags of 80 lb concrete mix or 445 bags of 60 lb. At this volume, delivered ready-mix is usually cheaper and far less work than mixing bags.
Should I use bags or ready-mix for a 20x30 slab?
Ready-mix. Bags for this slab would cost about $2,171 in material and require mixing 26,720 lb by hand; a delivered order runs roughly $1,148 and arrives ready to pour.