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How many 50lb bags of concrete per fence post?

By Dan Reyes, Concrete finisher, 18 years Last reviewed

Bag yields come off the manufacturer data sheet. An 80 lb bag yields about 0.60 ft³, so a cubic yard (27 ft³) takes roughly 45 bags. A 60 lb bag is about 0.45 ft³ or 60 bags per yard; 50 lb is about 0.375 ft³ or 72 bags; 40 lb is about 0.30 ft³ or 90 bags.

Typical thickness
a hole one-third of the post height and three times the post widthfence post
Typical strength
3ASTM C39 at 28 days
Typical strength
3,000–4,000 psi21–28 MPa residential
Test age
28 daysASTM C39

Short version

Common mistakes

  • Skipping the cure — concrete hardens by hydration, and drying it out early costs strength permanently
  • Ignoring exposure class — freeze-thaw and deicing salt require air entrainment under ACI 318
  • Treating a jurisdiction-specific requirement as universal — frost depth, permits and code editions are set locally
Sources (4)
  1. NRMCA — Concrete in Practice series (accessed Mon Aug 17 2026 00:00:00 GMT+0000 (Coordinated Universal Time))
  2. ASTM International — C39/C39M — Compressive Strength of Cylindrical Concrete Specimens (accessed Mon Aug 17 2026 00:00:00 GMT+0000 (Coordinated Universal Time))
  3. American Concrete Institute — ACI 318 — Building Code Requirements for Structural Concrete (accessed Mon Aug 17 2026 00:00:00 GMT+0000 (Coordinated Universal Time))
  4. PCA — America's Cement Manufacturers — Cement and Concrete Basics (accessed Mon Aug 17 2026 00:00:00 GMT+0000 (Coordinated Universal Time))

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