How Deep Should Fence Posts Be?
Quick Answer
Fence posts should be buried 1/3 of the total post length, typically 24-36 inches deep. A 6-foot fence needs posts buried at least 24 inches with concrete.
The 1/3 Rule
The standard rule is to bury one-third of the total post length underground. For a 6-foot fence, use 9-foot posts with 3 feet (36 inches) buried. At minimum, posts should be 24 inches deep.
Recommended Depths
- 4-foot fence: 24 inches deep (6-foot posts)
- 6-foot fence: 30-36 inches deep (8-9 foot posts)
- 8-foot fence: 36-42 inches deep (10-12 foot posts)
Frost Line Considerations
In cold climates, fence posts must extend below the frost line to prevent heaving. The frost line ranges from 12 inches in the South to 72 inches in northern states. Check your local building code for exact depth requirements.
Setting Posts in Concrete
Fill the hole with 2-3 bags of quick-setting concrete per post. The hole should be 3 times the width of the post (typically 9-12 inches diameter for a 4x4 post). Set posts in dry concrete mix, then add water — this prevents the post from shifting while curing.
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