How Much Concrete for a 8x8 Slab?
A 8x8 ft slab (64 sq ft) poured 4 inches thick needs about 0.87 cubic yards of concrete, or 40 bags of 80-lb mix. Both figures include 10% extra for spillage and an uneven subgrade.
8x8 slab by thickness
| Thickness | Cubic yards | 80-lb bags | 60-lb bags | 40-lb bags | Weight |
|---|---|---|---|---|---|
| 4 in (typical patio) | 0.87 | 40 | 53 | 79 | 3,520 lb |
| 5 in | 1.09 | 49 | 66 | 98 | 4,400 lb |
| 6 in (driveway, heavy use) | 1.3 | 59 | 79 | 118 | 5,280 lb |
Volume = length × width × thickness ÷ 12 = 8 × 8 × 4 ÷ 12 = 21.3 cu ft (0.79 cu yd) before the 10% extra. Bag yields: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft, 40 lb ≈ 0.30 cu ft.
Bags or ready-mix?
For the 4-inch slab, 40 bags at an example $7 each is about $280, while 0.87 yards of ready-mix at an example $165 a yard is about $143 before delivery and any short-load fee. Prices vary a lot by region and supplier, so enter your own in the concrete calculator. Mixing 40 bags means moving about 3,200 pounds of dry mix, plus water.
Before you order
A 8x8 slab also needs a base: gravel under the concrete is measured in cubic yards too, so use the gravel calculator for a 4-inch base. Check the area with the square footage calculator if the space is not a perfect rectangle, and add the extra for forms that bow or ground that dips. Wire mesh or rebar, expansion joints and curing time are not included in these figures.
Frequently asked questions
How many bags of concrete do I need for a 8x8 slab?
For a 8x8 ft slab 4 inches thick you need about 40 bags of 80-lb mix, 53 bags of 60-lb mix or 79 bags of 40-lb mix. That includes 10% extra for spillage and an uneven subgrade. Without the extra, the slab is 21.3 cubic feet.
How many yards of concrete is a 8x8 slab?
A 8x8 slab at 4 inches is 0.79 cubic yards, or 0.87 cubic yards with 10% extra. At 5 inches it is 1.09 yards and at 6 inches 1.3 yards.
How much does a 8x8 slab of concrete weigh?
Normal-weight concrete weighs about 150 pounds per cubic foot, so a 8x8 slab 4 inches thick weighs roughly 3,520 pounds (1.76 tons), including the extra.
Should I use bags or ready-mix for a 8x8 slab?
At 40 bags (3,200 lb of mix) bags are manageable if you can mix in batches. Ready-mix is faster and gives a more even pour, but suppliers often charge a short-load fee for small orders.
Other slab sizes
Planning figures for a rectangular slab. Brands and delivery practices differ, so confirm quantities with your supplier.