How Many Bags of Concrete for a 6x12 Slab?
A 6 by 12 foot slab at 4 inches holds 24.00 cubic feet of concrete. How many bags of concrete for a 6x12 slab comes to 40 bags of 80 lb mix or 54 of the 60 lb size, before a spare bag or two for waste.
Concrete calculator →How the bag count is figured
- Area: 6 × 12 = 72 sq ft.
- Volume at 4 in: 72 × 0.333 = 24.00 cu ft.
- 80 lb bags: 24.00 ÷ 0.60 = 40.0, round up to 40.
- 60 lb bags: 24.00 ÷ 0.45 = 53.3, round up to 54.
Check the yield printed on your brand’s bag, since it varies a little. The concrete calculator handles other shapes.
Related: How Much Concrete for a 6x12 Slab?
Bags by thickness for a 6x12 slab
| Thickness | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| 3 in | 18.00 | 30 | 40 | 60 |
| 4 in | 24.00 | 40 | 54 | 80 |
| 5 in | 30.00 | 50 | 67 | 100 |
| 6 in | 36.00 | 60 | 80 | 120 |
Bags or a truck?
Bags win on small pads because there is no delivery or short-load charge. The tradeoff is labor: 40 bags of 80 lb mix is 3,200 pounds to lift, pour and mix. A small drum mixer keeps batches consistent, and a helper keeps the pour moving so the edges do not set before the middle.
Related: How Much Recycled Concrete Aggregate for a 6x12 Shed Base?
Before you mix
A small slab still needs a firm base. Compact the soil, add compacted gravel and set forms to the finished height. If the pad will hold an AC unit, a generator or a grill, keep the top a little above the surrounding grade so water does not pool against it. Mixing 40 bags takes time, so stage them next to the forms before you start.
Buying the bags
A pallet of 80 lb bags often holds around 40 to 42 bags, so this job is about 1 pallet or less. Buy one or two extra bags: returning an unopened bag is easier than running out mid-pour.
Questions people ask
How many 80 lb bags for a 6x12 slab?
About 40 bags at 4 inches thick.
How many 60 lb bags for a 6x12 slab?
About 54 bags at 4 inches thick.
How many bags for a 6x12 slab 6 inches thick?
About 60 bags of 80 lb mix or 80 of 60 lb.
How much does an 80 lb bag of concrete yield?
About 0.6 cubic feet of mixed concrete.
How thick should the base under the slab be?
About 4 inches of compacted gravel is common for residential slabs, more on soft or poorly drained soil.
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 2x4 Slab?
- How Many Bags of Concrete for a 4x10 Slab?
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