How many bags of concrete do I need?
Bag count depends on slab length, width, thickness, waste allowance, and the actual yield of the bag you are buying.
The basic process
- Measure the length and width of the slab or pad.
- Choose the concrete thickness, usually in inches.
- Use the bag yield printed on the product packaging.
- Add a waste or overage allowance.
- Round up to whole bags.
Use the Concrete Bag Calculator to do the math automatically.
Why thickness matters so much
A small thickness change can noticeably change bag count. A 10 ft × 10 ft slab at 4 inches thick uses far more concrete than the same slab at 3 inches thick. Uneven ground, low spots, and form setup can also increase the real volume.
Common mistakes
Using the wrong bag yield
Bag weights and mixes vary. Use the cubic-foot yield printed on the bag when possible.
Not rounding up
Running short during a pour is worse than having an extra bag or two left over.
Ignoring uneven depth
If the base is uneven, the average thickness may be higher than the planned slab thickness.