A wood privacy fence comes down to three numbers: post count, panel count, and concrete bag count. Get the spacing and depth right and the fence stands for 20-30 years. Get them wrong and posts heave, panels warp, and gates sag within five.

Post spacing — 8 ft is the standard

Wood fence posts go on 8 ft centers for almost every residential install. That matches standard panel kits and pre-cut rails. Vinyl fences run 6 or 8 ft depending on the panel system. Chain link can stretch to 10 ft on light-duty residential.

The post count math is simple: total length ÷ spacing, then add one for the closing post. A 100 ft run at 8 ft spacing = 13 spans → 14 posts. Plus extras for every gate (one extra post per gate, since gates need a hinge post and a latch post on adjacent panels).

The fence calculator handles all three counts automatically.

Concrete per post — depth matters more than width

The standard rule for a 6 ft wood privacy fence is 2 bags of 60-lb concrete per post in a 10 in wide hole, 2 ft deep. Tighter math:

  • 3 ft fence (picket): 1 bag per post, 18 in deep
  • 4-5 ft fence: 1 bag per post, 24 in deep
  • 6 ft privacy fence: 2 bags per post, 24-30 in deep
  • 8 ft tall: 2-3 bags per post, 36 in deep, plus anchor lag bolts in some jurisdictions

Frost depth changes the rules

Posts must be set below the frost line or they'll heave every winter. Frost depths by region:

  • Southern states (FL, TX, AZ, GA): 0-12 in — anchor depth is wind-driven, not frost
  • Mid-Atlantic, Mid-South: 12-24 in
  • Midwest, Northeast: 36-48 in
  • Northern Plains, New England, Mountain West: 42-60 in

Check your county's published frost depth before digging. The fence calculator's default depth assumes a moderate climate; adjust your concrete bag count accordingly. A 4 ft frost depth doubles the bag count from a 2 ft depth.

Gate posts get extra everything

A gate post takes the swinging weight of the gate plus every slam over its lifetime. Treat both gate posts as heavy-duty:

  • Use 6×6 posts (not 4×4) — minimum on any gate over 4 ft wide
  • Set 6-12 in deeper than field posts
  • Add 1-2 extra bags of concrete per gate post
  • Use longer hinges with through-bolts, not lag screws, for any gate over 5 ft wide

Common errors

Forgetting the extra closing post. Posts are 1 more than the number of spans, not equal. A 100-ft run at 8 ft spacing has 13 spans but 14 posts.

Skipping the gravel base. Drop 4-6 in of gravel into the bottom of every post hole before the post goes in. Gravel drains water away from the post bottom. Direct concrete contact with end-grain rots out a treated 4×4 in 8-12 years.

Mixing concrete too wet. Fence-post concrete is meant to set moist, not soupy. Pour the dry mix into the hole, run a stick around to settle it, then add water until the surface goes wet but you can still hold the post plumb without it sinking. Wet-mixed concrete shrinks more and pulls away from the post wall.

Quick FAQ

How many fence posts for 100 feet? At 8 ft spacing: 14 posts (13 spans + 1 end). Add 1 per gate.

Can I set fence posts without concrete? For temporary fences and dog runs, gravel-only set works. For any permanent fence over 4 ft tall, concrete is the standard for wind resistance and frost stability.

Do I need a building permit for a fence? Most jurisdictions require permits for fences over 6 ft tall (sometimes 7) and any fence with a vehicle gate. Pickets and short privacy fences usually don't need permits but always need to respect property setbacks.

Estimate only. The fence calculator uses standard 6 ft wood privacy fence assumptions. Frost depth, wind exposure, and local building codes change post spacing and concrete requirements — verify with your jurisdiction before digging.