Fencing Guide

How deep should fence posts be?

The 1/3 rule, concrete, and why clay soil makes depth critical.

By The T.A.P. Team · June 2024 · 5 min read

The rule of thumb for fence posts is to set them about one-third of the above-ground height into the ground — so for a standard 6-foot fence, roughly 2 feet deep, in concrete. In North Texas, getting this right matters even more than usual, because our expansive clay soil heaves posts that aren't set deep and solid. Depth, hole shape, and how you finish the concrete all decide whether a fence stands straight for 20 years or leans in 5.

Post-setting rules

Depth: ~1/3 of above-ground height
6-ft fence: ~2 ft deep
Set in concrete, below the movement zone
Crown the concrete so water sheds off
Wider hole at the bottom resists heave

The one-third rule

Set at least a third of the total post length in the ground. A 6-foot fence uses ~8-foot posts with about 2 feet buried; a taller fence needs proportionally deeper posts. Deeper is better for stability, especially for gate and corner posts, which take more load and should go deeper than line posts.

Concrete and hole shape

Set posts in concrete, not just tamped dirt, for a fence that resists wind and lasts. Dig the hole a bit wider at the bottom than the top (bell-shaped) so the concrete footing resists being pushed up by heaving soil. Add a few inches of gravel at the base for drainage so water doesn't pool against the post and rot it.

Why clay soil makes depth critical

DFW's expansive clay swells when wet and shrinks when dry, and that movement lifts and tilts shallow posts — the leading cause of leaning fences here. Setting posts deep enough (below the most active soil movement) and in a proper footing is the defense. It's why cutting depth to save time is a false economy in our soil.

Finish it right

Crown the concrete — slope the top away from the post — so water runs off instead of pooling at the wood. Use treated or cedar posts rated for ground contact, and let the concrete cure before hanging pickets or a gate. Done this way, the posts — the part that usually fails first — get the best shot at a long life. See wood fence lifespan.

Fence height	Post depth (rule of thumb)
4 ft	~1.5 ft
6 ft	~2 ft
8 ft	~2.5–3 ft
Gate/corner posts	Deeper than line posts
All posts	In concrete, crowned to drain

You can DIY

Dig ~1/3 the post height
Bell the hole wider at the bottom
Add gravel for drainage
Set in concrete, post plumb
Crown the concrete to shed water

Call a pro

Long or tall fence runs
Gate and corner posts
Rocky or difficult digging
Setting posts right in heaving clay
Any fence that keeps leaning

Best practice: depth and drainage beat everything

The posts are the part of a fence that fails first, and depth plus drainage decide their fate. Set them a third of the way in, in a properly shaped concrete footing crowned to shed water, using ground-contact-rated wood. In our expansive clay, that's the single biggest thing separating a fence that stays straight for 20 years from one you're resetting in 5. Never shortcut the posts.

Setting posts in North Texas clay

Our expansive clay is unforgiving of shallow, poorly-set posts — it heaves them until the fence leans. We set posts to proper depth in crowned concrete footings across Plano, Allen, and McKinney, so fences stand straight for the long haul. See our fence installation team.

The short version

Set fence posts about one-third of their above-ground height deep.
A 6-foot fence needs posts roughly 2 feet in the ground.
Set them in concrete, not just packed dirt, for wind and longevity.
Bell the hole wider at the bottom so the footing resists heaving.
Crown the concrete to shed water and use ground-contact-rated wood.
In DFW's clay soil, proper depth and drainage are what keep a fence from leaning.