How it’s calculated
A round column is a cylinder; a square column is a rectangular prism.
Example: four 12 in round tubes, 4 ft tall: π × 1² ÷ 4 × 4 = 3.1416 ft³ each, 12.566 ft³ for four (0.465 yd³). With 10% waste: 13.82 ft³ = 0.512 yd³, or ⌈13.82 ÷ 0.60⌉ = 24 bags of 80 lb mix.
Frequently asked questions
How many bags of concrete for a 12 inch Sonotube?
A 12 in tube holds about 0.785 ft³ per foot of height. At 0.60 ft³ per 80 lb bag that is about 1.3 bags per foot, so a 4 ft tube takes about 5.2 bags (buy 6).
How much concrete for a fence post hole?
Use the round shape with the hole diameter and depth, then subtract the post volume if you want to be exact. Most people simply round up.
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Sources
- QUIKRETE Concrete Mix product data sheet (bag yields) — QUIKRETE Companies
- Topics in Concrete — American Concrete Institute
- NIST Handbook 44, Appendix C: Units of Measurement — U.S. National Institute of Standards and Technology
Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.
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