How Many Bags of Concrete for a 3x3 Slab?
A 3 by 3 foot slab at 4 inches holds 3.00 cubic feet of concrete. How many bags of concrete for a 3x3 slab comes to 5 bags of 80 lb mix or 7 of the 60 lb size, before a spare bag or two for waste.
Concrete calculator →How the bag count is figured
- Area: 3 × 3 = 9 sq ft.
- Volume at 4 in: 9 × 0.333 = 3.00 cu ft.
- 80 lb bags: 3.00 ÷ 0.60 = 5.0, round up to 5.
- 60 lb bags: 3.00 ÷ 0.45 = 6.7, round up to 7.
Check the yield printed on your brand’s bag, since it varies a little. The concrete calculator handles other shapes.
Related: How Much Sand for a 3x3 Sandbox?
Bags by thickness for a 3x3 slab
| Thickness | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| 3 in | 2.25 | 4 | 5 | 8 |
| 4 in | 3.00 | 5 | 7 | 10 |
| 5 in | 3.75 | 7 | 9 | 13 |
| 6 in | 4.50 | 8 | 10 | 15 |
Bags or a truck?
At 0.11 cubic yards, this pad is well under the point where a ready-mix truck starts to make sense. Many plants charge a small-load fee on tiny orders, so bags are often cheaper here, and a rented mixer makes 5 bags manageable for two people.
Related: How Many Bags of Concrete for a 10x10 Slab?
Before you mix
Dig out sod and soft soil, compact the bottom and add a few inches of compacted gravel. Set 2x4 forms level or with a slight slope for drainage, stake them every couple of feet and check the diagonals so the pad is square. Mixing 5 bags takes time, so stage them next to the forms before you start.
Buying the bags
Most stores stock 40, 60 and 80 lb bags. The 80 lb size means fewer bags to open, while 60 lb bags are easier to carry. Either way, buy a spare or two; a short pour is worse than a leftover bag.
Questions people ask
How many 80 lb bags for a 3x3 slab?
About 5 bags at 4 inches thick.
How many 60 lb bags for a 3x3 slab?
About 7 bags at 4 inches thick.
How many bags for a 3x3 slab 6 inches thick?
About 8 bags of 80 lb mix or 10 of 60 lb.
How much does an 80 lb bag of concrete yield?
About 0.6 cubic feet of mixed concrete.
When is bagged concrete practical?
Usually for jobs under about a cubic yard. Beyond that, mixing dozens of bags by hand gets slow and batches may not blend well.
Related guides
- How Much Area Does a Yard of Concrete Cover?
- How Many Bags of Concrete in a Yard? 40, 60, 80 lb
- Gravel Base Under a Concrete Slab: Depth and Tons
- How Many Yards in a Concrete Truck? Mixer Sizes
- Concrete Short Load Fee: What It Is and How to Cut It
- 60 lb vs 80 lb Concrete Bags: Yield, Count, and Cost
- Rebar vs Wire Mesh in a Slab: Which One to Use
- How Many Bags of Concrete for a 2x2 Slab?
- How Many Bags of Concrete for a 2x3 Slab?
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