How Much Concrete for a 24x36 Slab?
A 24×36 ft slab covers 864 sq ft. At the standard 4-inch thickness it needs 10.67 cubic yards of concrete – about 528 bags of 80 lb mix including 10% extra. Adjust the thickness below for your project.
Concrete for a 24x36 slab by thickness
| Thickness | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags | Ready-mix cost* |
|---|---|---|---|---|---|
| 4 in | 10.67 | 11.73 | 528 | 704 | $1,936 |
| 5 in | 13.33 | 14.67 | 661 | 881 | $2,420 |
| 6 in | 16 | 17.6 | 793 | 1056 | $2,904 |
*At about $165 per cubic yard before delivery and short-load fees. Bag counts include 10% extra.
How it is calculated
24 ft × 36 ft × (4 in ÷ 12) = 288 cu ft
288 cu ft ÷ 27 = 10.67 cubic yards
80 lb bags = 288 × 1.10 ÷ 0.60 = 528
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 24x36 slab?
A 24x36 slab (864 sq ft) needs 10.67 cubic yards at 4 inches thick, 13.33 yd³ at 5 inches and 16 yd³ at 6 inches, before waste.
How many bags of concrete for a 24x36 slab?
At 4 inches thick with 10% extra, you need about 528 bags of 80 lb concrete mix or 704 bags of 60 lb mix.
Should I use bags or ready-mix for a 24x36 slab?
At 11.7 cubic yards, ready-mix delivery is usually faster and more consistent than mixing 528 bags by hand. Many suppliers charge a short-load fee under 3–4 yards.