How deep should fence posts be?

Last reviewed 2026-06-06

A fence is only as strong as its posts. Here is how deep to set them, and how much concrete each hole needs.

Most failed fences fail at the posts — set too shallow, they lean and lift. The good news is the rules are simple, and getting them right makes the difference between a fence that lasts decades and one that wobbles in the first winter.

The one-third rule

A reliable starting point: bury about one-third of the post’s above-ground height. So a 6 ft tall fence wants posts set roughly 2 ft deep, meaning you buy 8 ft posts. Taller or more wind-exposed fences should go deeper.

Mind the frost line

In cold climates, set the bottom of the hole below your local frost line. If the post base sits within the freeze zone, the ground heaves each winter and pushes the post up over time. Your local building department can tell you the frost depth.

Hole width

A common rule is a hole about three times the post’s width — so a 4×4 post sits in a roughly 10–12 inch diameter hole. Wider holes hold more concrete and give a stronger footing for gate posts and corners.

Gravel first, then concrete

Add a few inches of gravel at the bottom of each hole so water drains away from the post base — this dramatically slows rot in wood and rust in steel. Set the post on the gravel, brace it plumb, then pour concrete around it (fast-setting post mix is easiest).

How much concrete per post?

It depends on the hole and post size, but a typical 10-inch, 24-inch-deep hole around a 4×4 post needs about a cubic foot — roughly two 80 lb bags. The post hole concrete calculator works out the exact bags for your sizes and number of holes, and the fence calculator gives you the post count.

Calculators for this

• Fence Calculator — Posts, rails and pickets for a fence run.
• Post Hole Concrete Calculator — Bags of concrete to set fence or deck posts.