6x6 Fence Post Concrete Calculator — Bags Per Heavy Post
Calculate concrete bags per 6×6 wood post for gate posts, corner posts, and heavy structural fence applications. Returns 60 and 80-pound bag counts.
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.
6×6 posts are the heavy-duty cousin of the standard 4×4 — used at gates, corners, terminal ends, in 8 ft tall privacy fences, and along high-wind property lines. The cross-section is nearly triple a 4×4 in moment of inertia, so a 6×6 resists lateral force with roughly 3× the stiffness.
This calculator estimates concrete for 6×6 posts including the proper displacement subtraction. A 6×6 buried 36 inches displaces 0.63 cu ft of concrete inside the hole — that's a full bag of 80 lb mix per post that you should NOT order.
How to Calculate Concrete for a 6x6 Fence Post
Concrete per 6×6 post (cu ft) = π × (Hole D ÷ 24)² × Depth × 12 − (5.5 ÷ 12)² × Buried Depth × 12. Bags 80 lb = ⌈Concrete ÷ 0.6⌉.
6×6 Post Common Configurations
- 14 inch hole × 36 inch deep: 2.21 cu ft net concrete ≈ 4 bags 80 lb. Typical gate or corner post.
- 16 inch hole × 42 inch deep: 3.08 cu ft ≈ 6 bags 80 lb. Heavy gate post or 8 ft tall fence corner.
- 14 inch hole × 48 inch deep (cold climate): 2.94 cu ft ≈ 5 bags 80 lb.
- 18 inch hole × 48 inch deep: 4.40 cu ft ≈ 8 bags 80 lb. Engineered or extra-heavy gate posts.
Frequently Asked Questions
When do I use a 6x6 fence post instead of 4x4?
6x6 posts are used at gate locations, fence corners, end posts, very tall (8+ ft) fences, and along property lines exposed to high wind. A 6x6 has nearly 3× the lateral strength of a 4x4 — worth the extra cost where loads concentrate.
How many bags of concrete per 6x6 post?
For a 6×6 post in a 14 inch hole 36 inches deep: 4 bags of 80 lb fast-set per post. For a heavier gate post in a 16 inch × 42 inch hole: 5-6 bags.
How deep should a 6x6 gate post be set?
36-42 inches minimum, or below frost line plus 1/3 of above-grade height. Gate posts swing heavy loads daily — deeper is always better. In freeze zones, 48 inches is common.
Should I use rebar in a 6x6 post hole?
For corner and gate posts in tall fences, yes — a vertical #4 bar inserted before pouring concrete improves lateral resistance dramatically. For straight-run 6x6 posts in light-wind areas, rebar is optional.
How is the post displacement different from a 4x4?
A 6x6 nominal post is actually 5-1/2 × 5-1/2 inches — it displaces 0.21 sq ft of hole cross-section vs 0.085 sq ft for 4x4. Over 36 inches of buried depth: 0.63 cu ft of concrete displaced (vs 0.255 for a 4x4 at 32 inches).
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 →