Concrete for a 20x24 Slab
Order 6.52 yd with 10% waste — or 267 × 80 lb bags / 356 × 60 lb bags.
By thickness
| Thickness | Cubic yards | +10% waste | 80 lb bags | Typical use |
|---|---|---|---|---|
| 4" | 5.93 | 6.52 | 267 | Patio, shed pad, walkway |
| 5" | 7.41 | 8.15 | 334 | Light vehicle traffic |
| 6" | 8.89 | 9.78 | 400 | Driveway, garage |
Bags or the truck?
For this 480 sq ft slab at 4": bags ≈ $1,736 (267 × 80 lb — that's 21,360 lb of mixing) vs ready-mix ≈ $919 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 20x24 slab?
A 20x24 slab at the standard 4-inch thickness needs 5.93 cubic yards of concrete — order 6.52 yards with a 10% waste margin. At 6 inches it needs 8.89 yards.
How many bags of concrete for a 20x24 slab?
At 4 inches thick: 267 bags of 80 lb concrete mix or 356 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 20x24 slab?
Ready-mix. Bags for this slab would cost about $1,736 in material and require mixing 21,360 lb by hand; a delivered order runs roughly $919 and arrives ready to pour.