How Many Bags of Concrete Do I Need?
Enter your project size and pick a bag weight — we'll tell you the exact number of bags to buy, rounded up and including a waste margin.
You need about
— bags
- Cubic yards: —
- 80 lb bags equivalent: —
How many bags — the math
volume (cu ft) = length × width × (thickness ÷ 12). Each bag yields a fixed volume:
an 80 lb bag ≈ 0.60 cu ft, a 60 lb bag ≈ 0.45 cu ft, and a
40 lb bag ≈ 0.30 cu ft. We divide your total volume by the chosen bag yield,
round up, then add your waste margin.
Most home-center mixes are 80 lb, so that's the default. If you're mixing by hand or have a smaller drill, 60 lb bags are easier to handle; 40 lb bags suit small repairs.
Concrete bag FAQ
How many 80 lb bags of concrete do I need for a 10x10 slab?
A 10x10 slab at 4 inches thick needs about 56 80 lb bags before waste. With 10% waste, buy about 62 bags.
How much concrete does a 60 lb bag make?
A standard 60 lb bag yields about 0.45 cubic feet of mixed concrete.
Should I add extra concrete for waste?
Yes. For most DIY slabs, 10% is a sensible margin. Use 15% if the ground is uneven or you are mixing by hand for the first time.
How many 80 lb bags equal one cubic yard?
One cubic yard is 27 cubic feet, so it takes about 45 80 lb bags.
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Last updated: 2026-09-09