How much concrete for a 8 x 8 slab?
Short answer
- A 8 x 8 ft slab is 64 square feet. At 4 inches thick it needs 0.79 cubic yards (21.3 cubic feet) of concrete.
- With 10% extra, buy 40 bags of 80 lb, 53 bags of 60 lb or 79 bags of 40 lb premixed concrete.
- It's typically a small shed base or a landing.
Concrete for a 8 x 8 slab at 4, 5 and 6 inches
Bag counts include 10% extra for uneven ground and spillage. Cubic yards are shown without extra so you can compare quotes.
| Thickness | Cubic yards | 80 lb bags | 60 lb bags | 40 lb bags | Weight with extra |
|---|---|---|---|---|---|
| 4 in | 0.79 | 40 | 53 | 79 | 1.6 to 1.8 tons |
| 5 in | 0.99 | 49 | 66 | 98 | 2.1 to 2.2 tons |
| 6 in | 1.19 | 59 | 79 | 118 | 2.5 to 2.6 tons |
Open this slab in the concrete calculator to change the size, thickness, waste or bag size.
How the math works
8 ft × 8 ft × 4 in ÷ 12 = 21.3 cubic feet. Divide by 27 to get 0.79 cubic yards. Add 10% and you have 23.5 cubic feet. An 80 lb bag of premixed concrete yields about 0.60 cubic feet, so 23.5 ÷ 0.60 rounds up to 40 bags.
Bags or ready-mix?
At 0.79 cubic yards, a 4 inch 8 x 8 slab is a reasonable size to mix from bags.
Forms and gravel base
The slab's edge is 32 feet, so that's how much form board you need around it, plus stakes. Under it, Quikrete's patio steps call for 5 inches of loose gravel tamped down to 4. For a 8 x 8 slab that's 26.7 cubic feet of loose gravel, about 0.99 cubic yards or 1.4 tons at 105 lb per cubic foot. The slab planner adds rebar or mesh and totals the cost with your local prices.
Other slab sizes
- 4 x 4 slab16 sq ft, typically a small pad for an AC unit, trash cans or a grill.
- 4 x 8 slab32 sq ft, typically a short walkway section or a stoop.
- 6 x 6 slab36 sq ft, typically a hot tub pad or a small landing.
- 8 x 10 slab80 sq ft, typically a shed base or a small patio.
- 10 x 10 slab100 sq ft, typically a small patio or a shed base.
- 10 x 12 slab120 sq ft, typically a patio or a 10 x 12 shed base.