How Deep Should a Fence Post Be Buried?

Your fence post should be buried at 1/3 to 1/2 of the height above the ground. For example, if you’re building a 6-foot fence, the underground portion of your post needs to be 2 to 3 feet. Meanwhile, the footing hole should be three times the post diameter. To keep the post hole sizes consistent, use a power auger for the digging. If you have loose soil, live in a windy climate, or need to set a gate post, you’d want to dig even deeper.

Fence Post Hole Depth Guidelines

Whether you're installing a picket or panel fence post, dig your hole deep enough to accommodate one-third to one-half of the aboveground height of your fence plus 3 to 6 inches of gravel. For example, a 6-foot-tall fence should have posts buried at least 24 inches deep, plus an extra 3 inches for gravel. Here are some basic guidelines.

Post Hole Width Guidelines

The width—or diameter—of your post hole should be three times the diameter of your post. Standard post diameter varies based on the type of fence, so you’ll need to measure, but here are some common sizes.

Post Hole Depth Guidelines for Gates

Gate posts require more stability because they have to handle the weight and movement of the gate. Dig your gate post holes deep enough to accommodate one-half of the aboveground height of your fence, plus a 6-inch layer of gravel.

Fence Post Depth and Frost Lines

If you live in an area that experiences freezing temperatures, your fence will be the most stable if you position the posts below the frost line. The frost line is the depth at which groundwater freezes in the soil. The type of soil around your home, its moisture content, and average temperatures in your area all contribute to the frost line. 

When you install fence posts above the frost line, the fence can be unstable due to the freezing and thaw of water in the soil. As water freezes, it expands. As it thaws, it contracts, potentially pushing the posts out of the soil. 

Your local fence code will most likely contain information about the required fence post depth to avoid frost damage. If it doesn't, and freezes occur in your area, a safe bet is to set the posts at least 24 inches deep. 

Tips to Make Sure Fence Posts Are Set Securely

Finding the fence post depth takes a little basic math. You’ll need a calculator and some measuring tape. These tips can help:

• Measure the height of your post, then divide the total height by two or three to get a general depth.

• Burying half the pole is the sturdiest option. It’s ideal for gate posts, fences made from heavier materials, loamy or clay soil, and climates with high winds.

• You can get away with burying a third of the pole if it’s a lightweight panel post and you have a sturdy soil type like sand, sandy loam, or gravel.

• Don’t forget to add 3 to 6 inches to your measurement for a layer of gravel. The more gravel, the better the drainage. This is especially important for wood posts, which can rot in moisture.

• Choose the right size nails for your fence pickets to prevent them from coming loose or splitting during installation. You’ll want 8d to 10d nails for setting pickets and 18d to 20d for posts.

• If you don't have experience, you should enlist a fence company near you.

Ways to Set Fence Posts

A properly installed fence post will last for several years, if not decades. Along with digging deeply enough and making the post hole the appropriate size, there are a few ways to fill the hole to increase stability.

• Add soil and gravel: Add 3 inches of gravel to the fence post hole to improve drainage, top the gravel with soil, and tamp it all down. Add 2 to 3 inches of gravel over the soil, then let it sit for several days. Tamp it down again before installing the pickets.

• Pour in concrete: Mix the concrete according to instructions and pour it into the post hole. To prevent water damage, apply silicone caulk between the post and concrete after the concrete dries.

• Apply expanding foam: Foam and concrete similarly help stabilize a fence post, but foam takes less time to set and cure. This option is best for lighter fences, such as those made from vinyl or mesh. Mix and apply the foam according to the package’s directions.

Signs Fence Posts Aren’t Buried Deep Enough

It's pretty easy to tell if a fence post isn't buried deeply enough. The post may be loose and easily moved. It may also start to lean, pulling the rest of the fence with it. Also, the bottom of your post needs to be set below the frost line. Otherwise, you will get frost heave over time and your post will eventually get pushed out of the ground after a frost due to soil contraption and movement.

Is It Possible to Reset Fence Posts?

You can reset a fence post if it wasn't installed correctly the first time. If the post was installed to the correct depth, you can fix any leaning or wobbliness by adding more soil around the post. 

Another option is to dig out around the posts and pour concrete into the hole to create a stronger base. If the posts are rotted or otherwise damaged, your best option may be to pull them up and replace them.

Installing a Fence Yourself vs. Hiring a Pro

Fence installation is not the most difficult DIY project, especially if you can find an experienced helper and live in an area that does not require a fencing permit. Typically, it’s a two-to-three-day job to build a fence, including any time you might need for post footings to set depending on the material. You can also install a no dig fence by yourself fairly easily.

However, we still recommend you to hire a pro if you’re building a taller privacy fence, or simply don’t want to deal with the time and labor. An experienced fence contractor ensures your new fence is properly installed and can handle all utility marking and permitting requirements. Generally, professional fence installation costs $1,856 to $4,750.