Concrete for a 30x40 Slab
Order 16.30 yd with 10% waste — or 667 × 80 lb bags / 889 × 60 lb bags.
By thickness
| Thickness | Cubic yards | +10% waste | 80 lb bags | Typical use |
|---|---|---|---|---|
| 4" | 14.81 | 16.30 | 667 | Patio, shed pad, walkway |
| 5" | 18.52 | 20.37 | 834 | Light vehicle traffic |
| 6" | 22.22 | 24.44 | 1000 | Driveway, garage |
Bags or the truck?
For this 1200 sq ft slab at 4": bags ≈ $4,336 (667 × 80 lb — that's 53,360 lb of mixing) vs ready-mix ≈ $2,296 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 30x40 slab?
A 30x40 slab at the standard 4-inch thickness needs 14.81 cubic yards of concrete — order 16.30 yards with a 10% waste margin. At 6 inches it needs 22.22 yards.
How many bags of concrete for a 30x40 slab?
At 4 inches thick: 667 bags of 80 lb concrete mix or 889 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 30x40 slab?
Ready-mix. Bags for this slab would cost about $4,336 in material and require mixing 53,360 lb by hand; a delivered order runs roughly $2,296 and arrives ready to pour.