FIELD NOTES // INSTALLATION

How Deep Should Fence Posts Be? Depth, Gravel and Post Length

For a general concrete-set post, QUIKRETE's Setting Posts in Concrete guide starts with a hole depth equal to one-third to one-half of the exposed post height, plus six inches for a gravel base. For six feet above ground, that is 24–36 inches of post embedment and a 30–42-inch excavation with that base.

By Get Your Fence On · SEPTEMBER 5, 2026 · Updated OCTOBER 20, 2026 · 7 MIN READ

A line of fence posts receding into morning mist across a field

Line posts carrying a fence across open ground. What decides whether they stay standing straight is the part of each post nobody photographs. Illustration only.

Those figures explain a common starting detail. The chosen fence system, soil, wind exposure, gate loads and applicable local requirements determine the actual foundation. Where frost-depth requirements apply, they must also be met. Use the approved detail for your project before buying posts or digging.

A quick depth table—with the reference point shown

Table 1. A quick depth table—with the reference point shown

Exposed post height

One-third to one-half below ground

Hole depth with a 6-inch base

4 ft / 48 in

16–24 in

22–30 in

5 ft / 60 in

20–30 in

26–36 in

6 ft / 72 in

24–36 in

30–42 in

If needed, scroll sideways or focus the table and use the arrow keys.

The table translates the proportions in QUIKRETE's illustrated guide . It is not a list of approved foundations. Keep the units and the six-inch base visible when comparing it with another instruction sheet.

QUIKRETE has other guides using different reference wording, including one-third of total post length. That is a different calculation . For 72 inches exposed, one-third of the total length buried means a 108-inch post with 36 inches buried. One-third of the exposed height means 24 inches buried. Do not combine fractions from different guides as though they mean the same thing.

Start with the system, then the site

An open chain-link run, a solid privacy panel and a wide gate do not apply the same forces to their supports. Post material, spacing, connections and exposure change the foundation decision. A proprietary driven system may use a different detail from a concrete-set wood or composite post.

Begin with the selected manufacturer 's instructions. Review the actual soil, grade, drainage and exposure, and confirm which local requirements apply to that installation. Where the site falls outside the published detail, obtain an appropriate design rather than combining unrelated rules of thumb.

The homepage's 30–36-inch planning reference describes a starting conversation, not a universal specification for every Missouri or Kansas fence.

Post embedment is different from excavation depth

Embedment measures how far the post extends below finished grade. Excavation depth reaches the bottom of the hole. A layer beneath the post makes the measurements different.

For example, 30 inches of post embedment above a 6-inch base requires a 36-inch excavation. That is arithmetic, not a recommendation that this footing suits your yard. An 8-foot post extending 6 feet above grade leaves 24 inches below grade; a deeper empty excavation cannot increase its length.

Show all three dimensions on the installation detail: finished post height, embedment and any allowance beneath it. Then choose a post length compatible with the complete assembly.

A fence wire anchored to a weathered concrete post

What holds a fence up is the part below grade: embedment, hole width and the footing detail. Illustration only.

Why depth alone cannot describe resistance to movement

A fence transfers load through panels or fabric, connections, posts and foundations into the ground. The dimensions and condition of each part affect the result. For an excavated footing, width and shape matter alongside depth. For a driven post, the permitted post section, installation method and ground conditions matter.

QUIKRETE publishes general hole-sizing and setting guidance for its post projects. Use that as guidance for the applications described, not as engineering approval for every fence. QUIKRETE setting-post guide .

Loose fill, obstructions or unexpected ground can require a revised approach. Establish how a changed condition will be assessed and approved before installation continues.

Check the local frost requirement

Freezing conditions can affect foundations. The design response depends on local conditions, the foundation type and the requirements applicable to the fence. A frost-depth map or building-foundation provision is not automatically the complete detail for every fence system.

Ask which local requirement and manufacturer instruction support the proposed foundation. Avoid claims that every shallow post will move after a predictable number of winters. That certainty requires evidence about conditions this article cannot inspect.

Gates and corners deserve their own detail

A gate support carries moving weight as well as environmental loads. Its required section, reinforcement, footing and hardware should follow the actual gate design. Some systems call for a different support at the hinge side; others use a qualified detail shared with adjacent supports.

Ask the estimator to show the gate opening, leaf dimensions , support, hinges and operating clearance together. A rule that every gate post must be a fixed amount deeper is less useful than a documented detail matched to the assembly.

Calculate post length before purchasing

Suppose a design requires the top of a post to stand 72 inches above finished grade and its embedment to be 36 inches. The simple combined length is 108 inches, or 9 feet, before any product-specific allowance, cut or cap detail. An 8-foot post cannot provide both of those stated dimensions.

Now add a 6-inch base beneath the post. The excavation reaches 42 inches below grade while the post still embeds 36 inches. It is a dimensional example, not an approved footing design.

Write the reference grade clearly. If the site will be regraded, decide which finished level the dimensions use. Otherwise, a correct measurement from temporary soil can become a different embedment after material is removed or added. Any grade change should also be reviewed for its effect on drainage, exposure and adjacent construction .

Measure the hole the detail requires

An excavated hole may be described by nominal auger size, finished diameter, shape and depth. Those descriptions are not always identical. Ask which dimensions the proposed installation detail requires and how they will be checked in the actual ground.

A hole that encounters rock or loose fill can differ from the planned dimensions. The response should follow the selected design and site assessment, not an improvised rule that extra width always replaces depth. The surrounding material and support mechanism matter.

Record the foundation method too. A driven post has no excavated concrete collar unless the specific system includes one. Comparing only a hole diameter between driven and concrete-set proposals would miss the method each uses to transfer load.

Soil changes the support question

The same post geometry can interact differently with firm ground, loose fill, rock or persistently wet conditions. A site description should distinguish what is observed from what remains uncertain. A published soil map can inform questions without establishing the conditions at every post location.

When unexpected material appears, ask what the selected system permits and whether another detail or professional review is needed. Record the finding and the agreed response. Do not let a fixed schedule turn an unsuitable condition into an undocumented exception.

A proposed change should also consider the rest of the layout. Moving a post can alter section length, gate clearance or the fence route. The response is therefore both a foundation and a layout decision, not merely a different place to make the same hole.

Plan for water around the post

The way water reaches and leaves the foundation affects exposure. A base material, surface shaping or other detail should belong to the selected installation and actual site. No single sketch proves that every soil will drain the same way.

Ask how the proposed detail handles surface water and the component's intended exposure. Avoid adding soil or mulch against a support simply to improve appearance. If water persistently collects along the line, identify that condition for assessment instead of assuming the footing will make it disappear.

For treated wood , material selection and field handling are separate from foundation geometry. A correctly sized hole does not upgrade an above-ground-only component to ground-contact service. Likewise, a suitable treatment label does not independently establish the structural adequacy of a footing.

A fence post cap and the fabric attached beside it