How Much Concrete for a 4x4 Slab?
A 4x4 ft slab (16 sq ft) poured 4 inches thick needs about 0.22 cubic yards of concrete, or 10 bags of 80-lb mix. Both figures include 10% extra for spillage and an uneven subgrade.
4x4 slab by thickness
| Thickness | Cubic yards | 80-lb bags | 60-lb bags | 40-lb bags | Weight |
|---|---|---|---|---|---|
| 4 in (typical patio) | 0.22 | 10 | 14 | 20 | 880 lb |
| 5 in | 0.27 | 13 | 17 | 25 | 1,100 lb |
| 6 in (driveway, heavy use) | 0.33 | 15 | 20 | 30 | 1,320 lb |
Volume = length × width × thickness ÷ 12 = 4 × 4 × 4 ÷ 12 = 5.3 cu ft (0.2 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, 10 bags at an example $7 each is about $70, while 0.22 yards of ready-mix at an example $165 a yard is about $36 before delivery and any short-load fee. Prices vary a lot by region and supplier, so enter your own in the concrete calculator. Mixing 10 bags means moving about 800 pounds of dry mix, plus water.
Before you order
A 4x4 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 4x4 slab?
For a 4x4 ft slab 4 inches thick you need about 10 bags of 80-lb mix, 14 bags of 60-lb mix or 20 bags of 40-lb mix. That includes 10% extra for spillage and an uneven subgrade. Without the extra, the slab is 5.3 cubic feet.
How many yards of concrete is a 4x4 slab?
A 4x4 slab at 4 inches is 0.2 cubic yards, or 0.22 cubic yards with 10% extra. At 5 inches it is 0.27 yards and at 6 inches 0.33 yards.
How much does a 4x4 slab of concrete weigh?
Normal-weight concrete weighs about 150 pounds per cubic foot, so a 4x4 slab 4 inches thick weighs roughly 880 pounds (0.44 tons), including the extra.
Should I use bags or ready-mix for a 4x4 slab?
At 10 bags (800 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.