Post Hole Concrete Calculator — Bags Per Hole
Estimate concrete bags needed to fill any post hole — fence, deck, mailbox, sign, or pergola posts. Returns 60 and 80-pound bag counts for any depth.
Enter Dimensions
Typically 1/3 of post height above grade
Results
Bags per Post
5bags
Total Bags
50bags
Volume per Hole
1.909cu ft
Concrete per post hole
Total Volume
19.09cu ft
All post holes combined
Editorial Standards
Each calculator is reviewed for formula accuracy, unit consistency, and alignment with current U.S. building practices before publication. We verify outputs against published engineering references and real-world project data. Learn more about our methodology.
Post holes — for fences, decks, pergolas, signs, mailboxes — share the same concrete sizing logic regardless of what's being set. The two variables are hole dimensions (diameter × depth) and post displacement (the volume of post buried inside the hole). Get both right and the bag count is exact.
This calculator handles any post-hole-concrete combination. For specific applications (4×4 wood post, metal pipe, deck post), see the focused calculators in the Concrete & Masonry cluster.
How to Estimate Concrete for Post Holes
Concrete (cu ft) = π × (Hole D ÷ 24)² × Depth × 12 − Post Volume. Bags 80 lb = ⌈Concrete ÷ 0.6⌉. Bags 60 lb = ⌈Concrete ÷ 0.45⌉.
Common Post Hole Concrete Quick Reference
- 4×4 post, 10″ × 30″ hole: 1.10 cu ft net = 2 bags 80 lb.
- 4×4 post, 12″ × 36″ hole: 1.86 cu ft = 4 bags 80 lb.
- 6×6 post, 14″ × 36″ hole: 2.21 cu ft = 4 bags 80 lb.
- 4×4 deck post, 12″ × 48″ hole: 2.61 cu ft = 5 bags 80 lb.
- 2-3/8″ metal pipe, 8″ × 30″ hole: 0.83 cu ft = 2 bags 60 lb.
- Mailbox post, 8″ × 24″ hole: 0.66 cu ft = 2 bags 60 lb.
Frequently Asked Questions
How much concrete fills a post hole?
Depends on hole size. A 10 inch diameter × 30 inch deep hole = 1.36 cu ft = 3 bags of 60 lb or 2-3 bags of 80 lb fast-set concrete. Larger holes scale proportionally.
Should the post displace concrete in the calculation?
Yes — for wood posts, subtract the buried portion of the post from the hole volume. A 4×4 (3.5 inch actual) buried 30 inches displaces 0.27 cu ft. For hollow metal posts, subtract only the pipe cross-section, not the full envelope.
How much concrete for a deck post hole?
Deck post holes are typically larger and deeper than fence post holes — 10-12 inch diameter × 36-48 inch deep. Plan 3-5 bags of 80 lb fast-set per deck post (varies with frost depth).
What types of post holes does this calculator cover?
Any cylindrical post hole: fence posts (wood, metal), deck posts, pergola posts, sign posts, mailbox posts, and shade structure piers.
Should I use fast-set or standard concrete?
Fast-set (Quikrete fast-set or similar) is the easier choice for most post-setting — pour dry, add water, post is rigid in 20-40 minutes. Standard 4000 psi takes 24+ hours and requires bracing.
Looking for the general calculator?
Calculate how many bags of concrete you need per fence post hole. Supports 4×4 and 6×6 wood posts plus metal pipe posts in standard hole sizes.
Open the Concrete Fence Post Calculator: Bag Count →