Building a wood privacy fence defines property boundaries, enhances curb appeal, and provides security for families and pets. Accurate material calculation prevents multiple trips to lumber yards and ensures consistent board quality throughout your project. This guide helps US homeowners and contractors estimate posts, rails, pickets, and concrete for residential wood fencing.

Post Spacing: The 6-Foot vs 8-Foot Decision

Fence posts anchor the entire structure and determine material costs, structural integrity, and installation labor. Post spacing (distance between post centers) is the most critical planning decision.

6-Foot Spacing (Stronger, Premium):

• Best for tall fences (6-8 feet) and high-wind areas
• Maximum structural rigidity—resists warping and leaning
• Recommended for heavy gates (double-wide, metal-framed)
• Requires 33% more posts than 8-foot spacing (higher cost)
• Standard for commercial and HOA-required installations

8-Foot Spacing (Standard, Economical):

• Most common residential fence spacing in US
• Adequate for standard 4-6 foot privacy fences
• Horizontal rails must be 2×4 lumber minimum (not 2×3)
• Saves 25% on posts and concrete vs 6-foot spacing
• Not recommended for areas with 50+ mph wind ratings

Calculate posts needed: Fence length (ft) ÷ Spacing (6 or 8) = sections. Add 1 for end post. Example: 100-foot fence with 8-ft spacing: 100 ÷ 8 = 12.5 sections = 13 sections + 1 end = 14 posts total.

Standard post sizing: Use 4×4 pressure-treated posts for residential fences up to 6 feet tall. For 8-foot privacy fences, upgrade to 6×6 posts for structural stability. Calculate post length: Fence height + 2-3 feet (buried depth).

Calculating Concrete for Post Setting

Fence posts must be set in concrete to prevent frost heave, wind damage, and rotational movement. The 1.5 bags per post rule is the industry standard for 4×4 posts in 8-12 inch diameter holes.

Standard concrete requirements:

• 4×4 posts: 1-1.5 bags of 50lb fast-setting concrete per post
• 6×6 posts or gate posts: 2-3 bags per post (larger diameter holes)
• Corner posts: 2 bags (increased stress requires extra stability)

Proper post hole dimensions:

Depth: Bury 1/3 of total post length. 6-foot fence (with 8-foot posts) needs 2-2.5 feet burial depth. Always dig below frost line in northern climates (check local codes).

Diameter: 8-12 inches for 4×4 posts, 12-16 inches for 6×6 posts. Wider holes provide better concrete collar and lateral support.

Installation method: Add 4-6 inches of gravel at hole bottom for drainage before setting post. Pour concrete around post, leaving top 3-4 inches for soil (prevents water pooling against wood). Slope concrete away from post or crown it above grade.

Picket Width Selection: 4-Inch vs 6-Inch Privacy Fences

Vertical pickets (fence boards) determine privacy level, material cost, and visual aesthetic. Standard dimensions use nominal lumber sizing (actual size is ~0.5" smaller).

1×4 Pickets (actual 3.5" wide):

• Most economical option—lowest material cost per linear foot
• Standard for semi-privacy and decorative fences
• With 0.5" spacing: ~4 inch coverage per board = 3 pickets per linear foot
• Lighter weight, easier DIY installation

1×6 Pickets (actual 5.5" wide):

• Premium privacy fence standard—fewer gaps, better security
• With 0.5" spacing: ~6 inch coverage = 2 pickets per linear foot
• More expensive but installs 33% faster (fewer boards)
• Heavier, more substantial appearance

1×8 Pickets (actual 7.25" wide):

• Used for board-on-board or shadowbox styles
• Maximum coverage with minimal gaps
• Heavy—requires robust 2×4 rails and shorter post spacing

Calculate pickets needed: Fence length (ft) × 12 (inches per foot) ÷ (Picket width + Gap spacing) = Total pickets.

Example: 100-foot fence with 5.5" pickets and 0.5" gap: 100 × 12 ÷ 6 = 200 pickets. Add 5-10% waste for cuts and damage.

Horizontal Rails and Fasteners

Rail configuration: Most residential fences use 2 horizontal rails (top and bottom) for 4-foot fences, or 3 rails (top, middle, bottom) for 6-foot fences. Rails span between posts and support pickets.

Standard rail lumber: 2×4 pressure-treated boards. Each section (between posts) needs 2-3 rails depending on fence height.

Calculate rails: Number of sections × rails per section = total rails. Example: 100-foot fence with 8-ft spacing = 13 sections × 3 rails = 39 rails (2×4 boards, 8 feet long).

Fasteners: Use galvanized or stainless steel screws/nails to prevent rust stains. Estimate:

• 2 screws per picket-rail connection (×2 or ×3 rails per picket)
• 4-6 screws per rail-to-post connection
• One 1-pound box of 2.5" deck screws per 50 linear feet of fence

Critical Fence Installation Tips

• String line method: Set corner/end posts first, pull string tight between them, then set intermediate posts to string for perfect alignment
• Pressure-treated lumber: Mandatory for posts and bottom rails (ground contact rating .40 or .60). Pickets can be cedar, PT pine, or composite
• Pre-stain or seal: Treat lumber before installation—easier than post-construction spraying and prevents weathering
• Gate placement: Install gate posts with 6×6 lumber or concrete-filled 4×4 posts for stability. Add diagonal brace to gate frame
• HOA and permits: Check property setback requirements (usually 6-12 inches from property line) and obtain permits for fences over 6 feet tall

Frequently Asked Questions