How Deep Should a 3 ft Fence Post Be
Find how deep to set fence posts and what length of post to buy.
Your result
Enter your numbers and press the button. Your result appears here.
How the depth is worked out
Depth in the ground = the greater of half the height above ground (the one-third rule) and the frost depth. Post length = height above ground + depth, rounded up to a stock length.
Example: a 3 ft fence needs posts 18 in into the ground, so buy 6 ft posts and dig 24 in deep.
Post depth at a glance
Worked out with the same settings as the calculator above, changing only the frost depth.
| Frost depth | Depth in ground | Post to buy | Hole depth |
|---|---|---|---|
| 0 in | 18 in | 6 ft | 24 in |
| 24 in | 24 in | 6 ft | 30 in |
| 36 in | 36 in | 6 ft | 42 in |
| 48 in | 48 in | 8 ft | 54 in |
| 60 in | 60 in | 8 ft | 66 in |
Rules of thumb
| Item | Typical |
|---|---|
| Depth in the ground | ⅓ of the post length, or below the frost line |
| Hole width | About 3 × the post width |
| Wood post spacing | 6 to 8 ft |
| Chain link line posts | No more than 10 ft |
| T-posts for barbed wire | 8 to 12 ft |
| Field fence | Wood posts 8–10 ft, T-posts 6–8 ft |
Common questions
How deep should a fence post be?
A common rule is to bury a third of the post's total length, which is half the height above ground. Quikrete's example is a post 6 ft above ground set 3 ft deep in a 9 ft post.
What about the frost line?
Where the ground freezes, set the bottom of the post below the frost line so frost cannot heave it. Frost depth ranges from almost nothing in the southern US to several feet in northern states and Canada; your building department can confirm it.
How wide should the hole be?
About three times the width of the post: roughly 10½ to 12 in for a 4×4 and 16 in for a 6×6.
Sources
- Quikrete, project calculator (post depth example): https://www.quikrete.com/calculator/