How Many Posts & Pickets for a 120 ft Wood Privacy Fence?
Building a 120-foot wood fence with 8-foot post spacing requires 17 posts (4×4 pressure-treated), 47 horizontal 2×4 rails, and 275 pickets (1×6 dog-ear) for full privacy. Each post hole requires 2 bags of fast-setting concrete (34 bags total) for 24"-30" in-ground footings.
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Fence Layout & Post Specs
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Fence Takeoff Schedule
| Component | Quantity | Unit | Est. Cost |
|---|---|---|---|
| 4"×4" Posts (8') | 17 | posts | $242 |
| Fast-Setting Concrete | 34 | bags (50 lb) | $233 |
| 2"×4" Rails (8') | 47 | rails | $360 |
| Dog-Ear Pickets (1"×6") | 275 | pickets | $811 |
| Exterior Fasteners | 5 | boxes (5 lb) | $160 |
| Gate Hardware Kits | 1 | kits | $42 |
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Material Takeoff & Accessory Checklist
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| Item / Specification | Category | Quantity | Unit Price | Total Est. | Supplier / Order |
|---|---|---|---|---|---|
4" x 4" x 8' Pressure-Treated Wood Posts Severe Weather Ground Contact posts (spaced 8' on-center) | primary | 17 posts | $242 | Home Depot | |
Fast-Setting Concrete Mix (50 lb Bag) Sets in 20-40 minutes without prior premixing (2 bags per post footing) | primary | 34 bags (50 lb) | $233 | Home Depot | |
2" x 4" x 8' Ground Contact Horizontal Rails 3 rails per section spanning post-to-post + gate framing | primary | 47 rails (8') | $360 | Local Supplier | |
1" x 6" x 6' Dog-Ear Fence Pickets Pressure-treated wood pickets, includes 5% cutting waste | primary | 275 pickets | $811 | Home Depot | |
1-5/8" Coated Exterior Star-Drive Wood Screws (5 lb Box) ACQ approved exterior screws for secure picket fastening without splitting | fastener | 4 box (5 lb) | $126 | Local Supplier | |
3" Exterior Heavy-Duty Structural Screws (5 lb Box) Fastens 2x4 rails securely to 4x4 posts with extreme shear resistance | fastener | 1 box (5 lb) | $34 | Local Supplier | |
Heavy-Duty Self-Closing Gate Hardware Kit Includes commercial T-hinges, gravity latch, handle, and anti-sag turnbuckle cable | accessory | 1 kits | $42 | Local Supplier |
Calculation Mechanics: Fence Post Spacing & Lumber Takeoff
Formulas adhere to ASTM standards, ACI 318 guidelines, and standard construction estimating practice.
Step-by-Step Derivation Breakdown:
- 1Compute structural post sections: 120 ft ÷ 8 ft spacing = 15 sections.
- 2Calculate total line, terminal & gate posts: 15 + 1 end post + 1 gate transitions = 17 posts.
- 3Calculate concrete footings: 2 bags (50-lb) per post hole = 34 bags (for 24"-30" frost depth).
- 4Calculate horizontal 2x4 rails: 15 sections × 3 rails + 2 gate frame rails = 47 rails (8 ft length).
- 5Calculate picket count: (120 ft × 12 in) ÷ 5.5 in effective width × 1.05 waste = 275 pickets.
Field Inspection & Trade Best Practices
- Post hole depth should equal 1/3 of the total post length (typically 24 to 30 inches deep in non-freezing zones, or below the local frost depth in northern climates).
- Always add 2-3 inches of crushed stone or gravel at the bottom of each post hole before pouring concrete to allow water drainage away from the wood end grain.
- Use hot-dipped galvanized or exterior-coated polymer screws rather than smooth framing nails to prevent unsightly black tannin bleed and fastener pullout over time.
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How This Takeoff Was Calculated
Step-by-Step Formula Breakdown:
Post Sections = ⌈120 ft ÷ 8 ft⌉ = 15. Posts = 15 + 1 end post + 1 gate post = 17 posts. Concrete = 17 posts × 2 bags = 34 bags. Pickets = (120 ft × 12 in) ÷ 5.5 in × 1.05 waste = 275 pickets.
Frequently Asked Questions for 120ft Property Border
How far apart should fence posts be placed?
Standard residential wood privacy fence posts are placed 8 feet apart on-center. In coastal areas or high-wind zones, 6-foot spacing is recommended to prevent rail sagging and wind shear damage.
How many bags of concrete do I need per fence post?
For a 6-foot privacy fence, holes should be 24 to 30 inches deep and 10 to 12 inches in diameter. This typically requires two 50-lb bags of fast-setting concrete per post hole.
How many horizontal rails are needed for a 6ft fence?
Building codes and structural best practices call for 3 horizontal 2x4 rails on any fence 6 feet or taller (top, middle, and bottom) to keep pickets from warping or bowing.