How Many Bags of Concrete for a 3x6 Slab?
A 3 by 6 foot slab at 4 inches holds 6.00 cubic feet of concrete. How many bags of concrete for a 3x6 slab comes to 10 bags of 80 lb mix or 14 of the 60 lb size, before a spare bag or two for waste.
Concrete calculator →How the bag count is figured
- Area: 3 × 6 = 18 sq ft.
- Volume at 4 in: 18 × 0.333 = 6.00 cu ft.
- 80 lb bags: 6.00 ÷ 0.60 = 10.0, round up to 10.
- 60 lb bags: 6.00 ÷ 0.45 = 13.3, round up to 14.
Check the yield printed on your brand’s bag, since it varies a little. The concrete calculator handles other shapes.
Related: How Many Bags of Concrete for an 8x10 Slab?
Bags by thickness for a 3x6 slab
| Thickness | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| 3 in | 4.50 | 8 | 10 | 15 |
| 4 in | 6.00 | 10 | 14 | 20 |
| 5 in | 7.50 | 13 | 17 | 25 |
| 6 in | 9.00 | 15 | 20 | 30 |
Bags or a truck?
Bags win on small pads because there is no delivery or short-load charge. The tradeoff is labor: 10 bags of 80 lb mix is 800 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 Many Bags of Concrete for a 6x10 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. Mix to a stiff, oatmeal-like consistency; extra water makes it easier to place but weaker.
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 3x6 slab?
About 10 bags at 4 inches thick.
How many 60 lb bags for a 3x6 slab?
About 14 bags at 4 inches thick.
How many bags for a 3x6 slab 6 inches thick?
About 15 bags of 80 lb mix or 20 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 an 8x12 Slab?
- How Many Bags of Concrete for a 10x10 Slab?
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