Concrete for a 4x8 Slab
Order 0.43 yd with 10% waste — or 18 × 80 lb bags / 24 × 60 lb bags.
By thickness
| Thickness | Cubic yards | +10% waste | 80 lb bags | Typical use |
|---|---|---|---|---|
| 4" | 0.40 | 0.43 | 18 | Patio, shed pad, walkway |
| 5" | 0.49 | 0.54 | 23 | Light vehicle traffic |
| 6" | 0.59 | 0.65 | 27 | Driveway, garage |
Bags or the truck?
For this 32 sq ft slab at 4": bags ≈ $117 (18 × 80 lb — that's 1,440 lb of mixing) vs ready-mix ≈ $136 delivered. Bags are competitive at this size. Prices are national ballparks — your local quote rules.
Adjust the numbers
Common questions
How much concrete do I need for a 4x8 slab?
A 4x8 slab at the standard 4-inch thickness needs 0.40 cubic yards of concrete — order 0.43 yards with a 10% waste margin. At 6 inches it needs 0.59 yards.
How many bags of concrete for a 4x8 slab?
At 4 inches thick: 18 bags of 80 lb concrete mix or 24 bags of 60 lb. At this size, bags are a reasonable DIY option.
Should I use bags or ready-mix for a 4x8 slab?
Either works at this size. Bags cost about $117; ready-mix about $136 after the short-load fee. Bags save money if your time is free; the truck saves your weekend.