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Fence Post Depth Calculator Guide
A fence is only as sturdy as its posts, and posts are only as sturdy as their footings. This calculator gives the recommended hole depth, total post length, and concrete per post for a stable fence.
Bury at least one-third of the post's above-ground height (and a minimum of 2 feet). In cold climates the hole must also go below the frost line, plus a few inches, to prevent heaving.
How Deep Should Fence Posts Be?
The common rule is to set posts at least one-third of their above-ground height into the ground, with 2 feet as a practical minimum for most fences. A 6-foot fence, for example, wants roughly 2 to 3 feet of post in the ground — deeper where the frost line is deep.
The Frost Line Matters
Where the ground freezes, water in the soil expands and can push shallow posts upward over the winter. To avoid this, the bottom of the hole should sit below your local frost line. Frost depth varies widely by region, so check a local source before digging.
Hole Diameter and Concrete
A good rule is to make the hole about three times the width of the post, so a 4-inch post uses a 12-inch hole. This calculator estimates the concrete needed to fill the hole around the post, in 50-lb bags. Add a gravel base at the bottom of the hole for drainage.
Set corner and gate posts a little deeper than line posts, since they carry the most stress. Always confirm requirements with your local building code.
Related: Gravel Calculator, Cubic Yard Calculator, and Lumber Calculator.
Frequently Asked Questions
How deep should fence posts be?
Set posts at least one-third of their above-ground height into the ground, with a 2-foot minimum, and always below the frost line in cold climates.
How deep should a 6-foot fence post be?
A 6-foot fence typically needs about 2 to 3 feet of post in the ground, using the one-third rule, or deeper if the frost line requires it.
How wide should the post hole be?
Make the hole about three times the post's width, so a 4-inch post uses a 12-inch-wide hole to hold enough concrete for stability.
Do I need concrete for fence posts?
Concrete gives the most secure footing, especially for corner, gate, and tall fence posts, though some line posts can be set in compacted gravel.
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