How deep should fence posts be?
The fence height, soil, frost depth, and local requirements can change the specified depth.
The QUIKRETE instruction gives a depth of one-third to one-half of the post length above ground. Add 6 in for gravel.
| Fence height | Initial depth range | Minimum post length |
|---|---|---|
| 4 ft | 22 to 30 in | 5 ft 10 in |
| 5 ft | 26 to 36 in | 7 ft 2 in |
| 6 ft | 30 to 42 in | 8 ft 6 in |
| 8 ft | 38 to 54 in | 11 ft 2 in |
The minimum post length uses the smaller depth in the range. Local requirements can make a deeper hole necessary.
Calculate the hole depth
Multiply the above-ground fence height by one-third or one-half. Then, add 6 in for the gravel layer.
Add the hole depth to the fence height. This result is the minimum post length.
The QUIKRETE post-setting instruction gives this method. It also gives a hole width that is three times the post width.
Soil and frost requirements
Loose soil can make a larger hole or a tube form necessary. Frost movement can make a deeper hole necessary.
If the local code or project specification gives more depth, use that depth.
Post and gate loads
A tall fence has more wind load. A gate also puts a side load on the hinge post.
Use the specified post size and footing for a tall fence, a wide gate, or an exposed site.
Before excavation
Before you dig, identify the property line and the permit requirements.
In the United States, contact the 811 utility-location service before excavation. The service gives instructions for the location of utilities below ground.
Use the fence calculator to calculate post length, concrete, and bag quantity.
Important information
- Use the local frost-depth and fence requirements.
- Use the measured fence height above the ground.
- Do not start excavation before the utility-location process is complete.