How much concrete for a 4 x 4 slab?
Short answer
- A 4 x 4 ft slab is 16 square feet. At 4 inches thick it needs 0.2 cubic yards (5.3 cubic feet) of concrete.
- With 10% extra, buy 10 bags of 80 lb, 14 bags of 60 lb or 20 bags of 40 lb premixed concrete.
- It's typically a small pad for an AC unit, trash cans or a grill.
Concrete for a 4 x 4 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 | 0.2 | 10 | 14 | 20 | about 0.4 tons |
| 5 in | 0.25 | 13 | 17 | 25 | 0.5 to 0.6 tons |
| 6 in | 0.3 | 15 | 20 | 30 | 0.6 to 0.7 tons |
Open this slab in the concrete calculator to change the size, thickness, waste or bag size.
How the math works
4 ft × 4 ft × 4 in ÷ 12 = 5.3 cubic feet. Divide by 27 to get 0.2 cubic yards. Add 10% and you have 5.9 cubic feet. An 80 lb bag of premixed concrete yields about 0.60 cubic feet, so 5.9 ÷ 0.60 rounds up to 10 bags.
Bags or ready-mix?
At 0.2 cubic yards, a 4 inch 4 x 4 slab is a reasonable size to mix from bags.
Forms and gravel base
The slab's edge is 16 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 4 x 4 slab that's 6.7 cubic feet of loose gravel, about 0.25 cubic yards or 0.4 tons at 105 lb per cubic foot. The slab planner adds rebar or mesh and totals the cost with your local prices.