How Much Concrete for a 10x20 Slab?
A 10×20 ft slab covers 200 sq ft. At the standard 4-inch thickness it needs 2.47 cubic yards of concrete – about 123 bags of 80 lb mix including 10% extra. Adjust the thickness below for your project.
Concrete for a 10x20 slab by thickness
| Thickness | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags | Ready-mix cost* |
|---|---|---|---|---|---|
| 4 in | 2.47 | 2.72 | 123 | 163 | $448 |
| 5 in | 3.09 | 3.4 | 153 | 204 | $560 |
| 6 in | 3.7 | 4.07 | 184 | 245 | $672 |
*At about $165 per cubic yard before delivery and short-load fees. Bag counts include 10% extra.
How it is calculated
10 ft × 20 ft × (4 in ÷ 12) = 66.7 cu ft
66.7 cu ft ÷ 27 = 2.47 cubic yards
80 lb bags = 66.7 × 1.10 ÷ 0.60 = 123
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 10x20 slab?
A 10x20 slab (200 sq ft) needs 2.47 cubic yards at 4 inches thick, 3.09 yd³ at 5 inches and 3.7 yd³ at 6 inches, before waste.
How many bags of concrete for a 10x20 slab?
At 4 inches thick with 10% extra, you need about 123 bags of 80 lb concrete mix or 163 bags of 60 lb mix.
Should I use bags or ready-mix for a 10x20 slab?
At 2.7 cubic yards, ready-mix delivery is usually faster and more consistent than mixing 123 bags by hand. Many suppliers charge a short-load fee under 3–4 yards.