Guide
How deep to set fence posts
A third of the height above ground, at least 2 ft, and below the frost line.
Short answer
Set posts at least a third as deep as the fence is tall, never less than 24 in, and below the frost line where the ground freezes. For a 6 ft fence that is 24 in in mild climates, so an 8 ft post; in frost country 36 to 48 in, which takes a 10 ft post.
Depth and post length by fence height
| Fence height | Post depth | Post to buy |
|---|---|---|
| 3 ft | 24 in | 6 ft |
| 4 ft | 24 in | 6 ft |
| 5 ft | 24 in | 8 ft |
| 6 ft | 24 in | 8 ft |
| 8 ft | 32 in | 12 ft |
The third-of-the-height rule is about leverage: a post is a lever with the fence panel pushing on the top and the ground holding the bottom, and wind on a solid 6 ft fence is a large force. Gate posts carry a moving load as well, so set them 6 in deeper than the rest and a size larger.
Below the frost line
Where the ground freezes, water in the soil expands and lifts anything whose base sits in the frozen layer. Posts set above the frost line heave a little every winter and lean within a few years. The hole has to go below it, and in cold regions the frost depth, not the fence height, sets the post length.
| Region | Hole depth | Post to buy | 80 lb concrete bags |
|---|---|---|---|
| Gulf coast and southern Florida | 24 in | 8 ft | 2 |
| Mid-South and southern plains | 24 in | 8 ft | 2 |
| Mid-Atlantic and central plains | 30 in | 10 ft | 2 |
| Upper Midwest and Northeast | 42 in | 10 ft | 3 |
| Northern plains and mountain states | 48 in | 10 ft | 3 |
Is 2 ft deep enough?
For a fence up to 6 ft on firm soil where the ground does not freeze deeply, yes: 24 in is the working minimum. It is not enough for an 8 ft fence, which needs about 32 in, for gate posts, for loose or sandy soil, or anywhere the frost goes deeper than 2 ft. Call 811 before digging any hole: it is free, and buried lines are often shallower than people expect.