How Much Concrete for a 12x12 Slab?
A 12×12 ft slab covers 144 sq ft. At the standard 4-inch thickness it needs 1.78 cubic yards of concrete – about 89 bags of 80 lb mix including 10% extra. Adjust the thickness below for your project.
Concrete for a 12x12 slab by thickness
| Thickness | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags | Ready-mix cost* |
|---|---|---|---|---|---|
| 4 in | 1.78 | 1.96 | 89 | 118 | $323 |
| 5 in | 2.22 | 2.44 | 110 | 147 | $403 |
| 6 in | 2.67 | 2.93 | 132 | 176 | $484 |
*At about $165 per cubic yard before delivery and short-load fees. Bag counts include 10% extra.
How it is calculated
12 ft × 12 ft × (4 in ÷ 12) = 48 cu ft
48 cu ft ÷ 27 = 1.78 cubic yards
80 lb bags = 48 × 1.10 ÷ 0.60 = 89
Which thickness do you need?
- 4 inches – patios, walkways, shed floors and most residential garage floors.
- 5–6 inches – driveways, hot tub pads, and garages for heavier trucks or RVs.
- Add 4–6 inches of compacted gravel base underneath and use rebar or wire mesh for slabs larger than about 10×10 ft.
Frequently asked questions
How many yards of concrete for a 12x12 slab?
A 12x12 slab (144 sq ft) needs 1.78 cubic yards at 4 inches thick, 2.22 yd³ at 5 inches and 2.67 yd³ at 6 inches, before waste.
How many bags of concrete for a 12x12 slab?
At 4 inches thick with 10% extra, you need about 89 bags of 80 lb concrete mix or 118 bags of 60 lb mix.
Should I use bags or ready-mix for a 12x12 slab?
At 2 cubic yards, ready-mix delivery is usually faster and more consistent than mixing 89 bags by hand. Many suppliers charge a short-load fee under 3–4 yards.