Concrete & Masonry
Concrete Bag Calculator
Use this concrete bag calculator for fence posts, deck posts, mailboxes, and other round post holes.
Estimated concrete
18 bags10.37 cubic feet with buffer9.42 cubic feet before bufferFormula
π × radius² × depth × number of holes = cubic feet of concrete
Check the yield printed on your bag. An 80 lb bag commonly yields about 0.6 cubic feet, but products vary.
Quick reference
| Project size | Common use | Planning note |
|---|---|---|
| 100 sq ft | Small bed or walkway | Good for testing bagged material prices |
| 250 sq ft | Medium garden or patio area | Bulk delivery may start making sense |
| 500 sq ft | Large lawn, driveway, or landscape zone | Measure carefully and add a buffer |
FAQ
How much concrete does an 80 lb bag make?
Many 80 lb concrete mix bags yield about 0.6 cubic feet. Always verify the yield on the product label.
Should I add extra concrete?
Yes. A 10% buffer helps cover uneven holes, spillage, and small measurement errors.
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