Concrete for a 15x15 Slab
Order 3.06 yd with 10% waste — or 125 × 80 lb bags / 167 × 60 lb bags.
By thickness
| Thickness | Cubic yards | +10% waste | 80 lb bags | Typical use |
|---|---|---|---|---|
| 4" | 2.78 | 3.06 | 125 | Patio, shed pad, walkway |
| 5" | 3.47 | 3.82 | 157 | Light vehicle traffic |
| 6" | 4.17 | 4.58 | 188 | Driveway, garage |
Bags or the truck?
For this 225 sq ft slab at 4": bags ≈ $813 (125 × 80 lb — that's 10,000 lb of mixing) vs ready-mix ≈ $506 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 15x15 slab?
A 15x15 slab at the standard 4-inch thickness needs 2.78 cubic yards of concrete — order 3.06 yards with a 10% waste margin. At 6 inches it needs 4.17 yards.
How many bags of concrete for a 15x15 slab?
At 4 inches thick: 125 bags of 80 lb concrete mix or 167 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 15x15 slab?
Ready-mix. Bags for this slab would cost about $813 in material and require mixing 10,000 lb by hand; a delivered order runs roughly $506 and arrives ready to pour.