For most people, around 1/3rd of the height of the post should be in the ground. If your post is 6 feet, then the fence post hole should be at least 2 feet. This is a general rule of thumb that you can follow for almost any situation. The long answer would take into consideration things like the width of the post, the type of soil you’re digging, and you may need to consider the width of the hole as well.
In this post, we’ll be taking a more in-depth look at how deep a fence post hole should be.
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Examine the height of your fence post
The height of your post is the most important factor when it comes to digging a fence post hole. If the hole is too shallow then you’ll find that your fence will be wobbly and can even tip over. If it’s too deep, then you’ll be doing a lot of extra digging for no reason and you may cause long-term issues in the soil and surrounding earth.
Here’s a rough idea of how deep your fence post hole should be:
- 4 feet fence post, at least 1.4 – 2 feet hole depth
- 6 feet fence post, at least 2 – 3 feet hole depth
- 7 feet fence post, at least 2.4 – 3.5 feet hole depth
- 8 feet fence post, at least 2.7 – 4 feet hole depth
- 10 feet fence post, at least 3.4 – 5 feet hole depth
In short, the depth of the fence post hole should be roughly a third of the length of the fence post but no more than half the length. Digging a little further is usually no issue, but it should
What about gate posts?
Gate posts usually need to be a little deeper than a regular fence post. This is because they need to withstand the extra weight of the gate and also the force of the gate’s movement. It’s also recommended to set gate posts with concrete for extra stability because the movement of the gate can eventually loosen the post.
So for gate post holes, we would suggest the minimum depth of a third of the gate post’s length, but have it supported by concrete. For extra stability, you can go up to half of the gate post’s length.
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Ground conditions and the frost line
Ground conditions are important to take into consideration. When performing any kind of construction project on your land, you absolutely need to do your due diligence and consult with municipal officials about your plans to build a fence around your property or land. There may be strict regulations to consider and you’ll also receive some advice regarding the land that you plan to dig holes into.
The last thing to consider is the frost line. This is used to describe the frost depth or freezing depth where groundwater in soil is expected to freeze. If your posts are above this line, then it can create problems in the future. Consult local codes to see what the depth of the frost line is and make sure your fence posts go below this depth.
Here are some examples of frost lines by state:
- South Carolina – 4 inches (the shallowest frost line in the US)
- California – 5 inches
- Missouri – 33 inches (the US average)
- New York – 50 inches
- Alaska – 100 inches (the deepest frost line in the US)
And here are some examples in Canada:
- Windsor – 40 inches
- Ottawa – 70 inches