Fence Post Depth and Spacing: How Deep and How Far Apart

Updated 2026-08-27 · Yardly

Bury at least one-third of the post and keep the bottom of the concrete 6 inches below the frost line. For a typical 6-foot fence that means a 9-foot post with 36 inches in the ground, spaced 6 to 8 feet apart. Get those two numbers right and the fence stays straight for decades; cut corners and it leans within a year.

The one-third rule

The widely used baseline is to bury one-third of the post’s total length. Fence posts are usually sold 3 feet longer than the fence height precisely to hit this ratio:

Buried depth = Total post length ÷ 3

Fence height	Total post length	Buried depth (1/3 rule)
4 ft	7 ft	28 in
6 ft	9 ft	36 in
8 ft	12 ft	48 in

Frost line overrides depth

The one-third rule is only your starting point. When soil freezes it expands and pushes posts upward (frost heave), so the concrete footing must sit at least 6 inches below the local frost line. Frost depths vary widely — roughly 0–12 inches across the Gulf Coast, 30–42 inches through the Mid-Atlantic, and 48–72 inches in the Upper Midwest.

Use whichever is greater: the one-third depth, or 6 inches below the frost line.

For a 6-ft fence in New England the one-third rule gives 36 inches, but if the frost line is 48 inches you’d set the footing at 54 inches — which means a roughly 10-ft-6-in post, not a 9-footer. Guides from fence manufacturers such as FenceTrac’s post-depth reference lay out the same one-third-plus-frost-line logic and stress checking local building code before you dig.

Spacing

Post spacing trades strength against material cost:

• Wood fence: 8 ft on center is standard; use 6 ft for fences over 6 ft tall, privacy styles, or exposed, windy sites.
• Chain link: commonly 10 ft on center.
• Corner and gate posts: go one size larger (6×6 instead of 4×4) and set them 6 inches deeper than line posts, because they carry the most torque.

Closer spacing adds rigidity but raises your post and concrete count proportionally, so match it to the wind load rather than maxing it out everywhere.

Concrete per hole

For a 4×4 post in a 10-inch-diameter hole, plan on 2 bags of 50-lb or 60-lb mix; a 6×6 post or 12-inch hole takes 3–4 bags. A 4-inch gravel layer at the bottom improves drainage and fights rot, and fast-setting concrete (e.g. QUIKRETE fast-setting mix) sets in 20–40 minutes without mixing — pour dry, add water, done.

A worked example

An 80-ft run of 6-ft wood fence at 8-ft spacing:

• Posts = (80 ÷ 8) + 1 = 11 posts
• Each 9-ft post, 36 in buried, 2 bags concrete → 22 bags
• Add 2 corner posts at 6×6, 3–4 bags each → ~6 extra bags
• Total ≈ 28 bags of 50-lb mix

Round up and buy a few spares; a short pour on the last hole is the most common avoidable mistake.

Keep reading

• Get exact holes and bag counts from our fence post concrete calculator
• Need the slab math for a related pad? See the concrete slab calculator
• Planning the whole build? Open the fence project planner

Frequently asked questions