Calculate wood privacy fence materials accurately: determine 4x4 line posts, horizontal 2x4 rails, vertical pickets, and footing concrete bag takeoffs.
Standard Fence Post Spacing (6-Foot vs. 8-Foot Bays)
Residential wood fences are framed with 4x4 pressure-treated posts set either 6 feet or 8 feet apart on center (OC):
• 8-Foot Spacing: Standard residential construction. Economical and uses standard 8-ft dimensional 2x4 rails without cutting.
• 6-Foot Spacing: Recommended for high-wind coastal zones, heavy 6-foot dog-ear cedar privacy fences, or heavy slope transitions to prevent rail sagging.
Calculating Posthole Depth and Concrete Bags
The longevity of any fence depends on posthole depth. The golden rule of fence posts is the 1/3 in ground rule:
For a standard 6-foot tall privacy fence, you must use 8-foot or 9-foot posts set a minimum of 24 to 36 inches deep (below the local frost line).
Concrete requirement: Each 4x4 post set in a 10-inch diameter hole requires 1.5 to 2 eighty-pound bags of fast-setting concrete mix.
| Fence Run (Linear Feet) | 4x4 Posts (@ 8ft OC) | 2x4 Rails (3 per bay for 6ft) | Pickets (5.5" Dog-Ear) | 80-lb Concrete Bags |
|---|---|---|---|---|
| 50 linear ft | 8 posts | 21 rails | 110 pickets | 16 bags |
| 100 linear ft | 14 posts | 39 rails | 220 pickets | 28 bags |
| 150 linear ft | 20 posts | 57 rails | 330 pickets | 40 bags |
| 200 linear ft (Full Yard) | 26 posts | 75 rails | 440 pickets | 52 bags |
Horizontal Rails and Fastener Requirements
• 4-Foot Tall Fences: Require 2 horizontal 2x4 rails per 8-ft section.
• 6-Foot Tall Privacy Fences: Require 3 horizontal 2x4 rails per 8-ft section to prevent pickets from warping or bowing under sun and rain.
Fasteners: Always use hot-dipped galvanized or 304/316 stainless steel ring-shank nails or exterior deck screws. Standard electro-galvanized or drywall screws will corrode and leave black tannin streaks down cedar and pressure-treated wood.
Frequently Asked Questions & Answers
Click any question below to expand quick answers, formulas, and expert tips.
How wide is a standard 6-inch fence picket?
Nominal 6-inch wood pickets actually measure 5-1/2 inches wide. If installed tight without gaps, you need 2.18 pickets per linear foot.
Should concrete be poured to the very top of the fence posthole?
Slope the top of the concrete collar slightly away from the wood post to shed water and prevent pooling rot at the ground line.
