Fence post hole concrete guide (depth, diameter, and layout)

Why post count is not just length / spacing

• Corners, ends, and gates add posts beyond simple spacing math.
• Gate posts often need heavier posts and more concrete.
• Sloped terrain and stepped panels can change layout and spacing.

Concrete volume example

Example: a 10 inch diameter hole at 36 inches deep is about 1.64 cu ft of concrete. Multiply by hole count and round up.

• Increase volume for bell-shaped or flared bottoms.
• Order extra if your holes are oversized or sloped.

Depth planning (frost and wind)

• Frost depth often sets the minimum hole depth in cold climates.
• Taller fences and windy sites usually need deeper or wider footings.
• Corner and gate posts carry higher loads and should be planned separately.

Concrete planning notes

Concrete volume depends on hole diameter and depth. Local frost depth and soil conditions can change requirements, so confirm local practice and code.

Hole size basics (depth and diameter)

There is no single "correct" hole size for every fence. Depth is driven by frost line guidance, fence height, wind load, and soil conditions. Diameter is driven by post size and the footing system you use.

Concrete volume math (quick method)

A post hole is often approximated as a cylinder: volume = pi * (radius^2) * depth. Convert to cubic feet, then convert to bags using your bag yield (or order ready-mix if the job is large).

Example: a 12 inch diameter hole that is 36 inches deep is radius 0.5 ft and depth 3 ft, so volume ~ 3.14 * (0.5^2) * 3 ~ 2.36 cu ft per hole (before gravel base or bell shapes).

• If you add a gravel base, subtract that depth from the concrete depth.
• Bell-shaped footings can increase volume beyond a simple cylinder estimate.
• Round up: running short mid-set is a big time penalty.

Concrete vs gravel set (why the system matters)

• Concrete-set posts are common for gates, corners, and higher loads (project dependent).
• Gravel set can drain well, but performance depends on compaction and soil conditions.
• If frost heave is a concern, drainage and depth planning are usually more important than perfect volume math.

Bell footings and gravel bases

• Bell-shaped footings can resist uplift but increase concrete volume.
• A compacted gravel base can improve drainage under the post.
• If you add gravel, subtract that depth from the concrete depth.

Setting posts (simple workflow)

• Lay out post locations first (corners, ends, gates), then string a line for straight runs.
• Dig holes and dry-fit posts to confirm height and alignment before mixing concrete.
• Brace posts plumb in two directions so they don’t move while concrete sets.
• Place concrete, rod/tamp to remove voids, then shape the top to shed water away from the post.

Drainage notes (frost heave and rot prevention)

Water management matters. Even a perfectly sized footing can perform poorly if water sits around the post. This is one reason some systems use a gravel base or focus heavily on depth and drainage details (project dependent).

• If you add a gravel base, compact it and keep the post stable before pouring concrete above it.
• Slope the finished concrete cap away from the post so water doesn’t pool at the wood/concrete interface.

Ordering and waste planning

• Calculate total concrete volume (per hole × number of holes) and add a buffer for over-excavation and bell shapes.
• If the job needs many bags, consider ready-mix or at least a consistent mixing plan so all batches are similar.
• Keep extra mix for small patches and to avoid stopping mid-set if one hole is larger than planned.

Common mistakes

• Not bracing posts plumb; a small lean is obvious once panels are attached.
• Mixing different consistencies from hole to hole (harder to set a consistent height).
• Leaving the top of the concrete flat so water pools around the post.

• Fence calculator
• Fence posts guide