Building a fence seems easy until you're standing in the middle of a home improvement aisle staring at a 6 foot fence post and realizing it’s actually the wrong size for a 6-foot fence. It’s a classic rookie mistake. Honestly, I’ve seen seasoned DIYers do it too. They want a six-foot-tall privacy screen, so they buy six-foot posts. Then they get home, dig a hole, drop the post in, and realize their fence is now only four feet tall because two feet of that expensive pressure-treated timber is buried in the dirt.
You have to think about the physics of wind load and soil tension. A fence is basically a giant sail. When a summer storm kicks up, that flat surface of cedar or vinyl catches every bit of force. If your post isn’t deep enough, the whole thing just tips over. It’s a mess.
The big 6 foot fence post misunderstanding
Most people searching for a 6 foot fence post are actually looking to build a 4-foot fence. That’s the golden rule of fencing: your post needs to be about 30% to 50% longer than the height of the fence above ground. If you’re using a true 6-foot post, you’re likely building a garden border or a decorative picket fence that sits waist-high.
If you actually want a 6-foot-tall privacy fence, you need 8-foot or even 9-foot posts.
Why does this matter so much? Frost heave. In places like Chicago or New York, the ground freezes and expands. If your post isn't set below the frost line—which is often 36 inches deep—the earth will literally spit your fence out over a few winters. You'll wake up in March and your perfectly straight line will look like a row of broken teeth.
Material choices: Beyond the basic 4x4
Not all posts are created equal. You’ve got options, and they aren't just about aesthetics; they’re about how much maintenance you want to do in five years.
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Pressure-Treated Pine is the workhorse. It’s cheap. It’s everywhere. But it has a nasty habit of warping. You buy a straight post, and three months later, it’s twisted like a pretzel. If you go this route, look for "Ground Contact" rated lumber. There’s a difference between "above-ground" and "ground contact" treatment levels (measured by the retention of chemicals like ACQ or Micronized Copper Azole). If you put an above-ground rated 6 foot fence post into wet soil, it’ll rot in less than five years.
Cedar is the premium choice. It smells great and resists rot naturally. But even cedar shouldn't touch the dirt directly if you want it to last decades. Most pros will tell you to use a metal post base or at least a heavy gravel footer to keep the "feet" of the cedar dry.
Then there’s Steel (PostMaster style). These are becoming huge in 2026. They’re galvanized steel U-channels that you can hide behind wood pickets. They don't rot. They don't warp. They don't care about moisture. They cost more upfront, but you’ll never have to dig them out and replace them.
The engineering of the hole
Digging is the worst part. Nobody likes it. But the hole is more important than the post itself.
A common mistake is making the hole too narrow. You want the diameter to be three times the width of the post. For a standard 4x4 (which is actually 3.5 inches by 3.5 inches), your hole should be about 10 to 12 inches wide. This allows for a thick "collar" of concrete to surround the wood.
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Don't just dump dry concrete mix into the hole and spray it with a hose. People do this all the time because of "fast-setting" bag marketing. It works okay, but for maximum structural integrity, mixing it in a wheelbarrow first ensures there are no pockets of dry powder at the bottom. Dry pockets lead to water collection. Water collection leads to rot. Rot leads to you spending your Saturday replacing a 6 foot fence post while your neighbors watch and judge.
To gravel or not to gravel?
Always use gravel. Put six inches of crushed stone at the bottom of the hole before the post goes in. This acts as a drainage well. Without it, the bottom of the post sits in a "concrete cup" that holds water against the end grain of the wood—which is the most absorbent part of the tree. It’s like putting a straw in a glass of water.
Real-world costs and availability
Prices fluctuate wildly based on your region. In the Pacific Northwest, cedar is relatively affordable. In the South, you're looking at pressure-treated pine as the standard.
Expect to pay:
- $12 - $18 for a pressure-treated 4x4x6.
- $25 - $40 for a Western Red Cedar 4x4x6.
- $30+ for heavy-duty vinyl or composite options.
Remember that a 6 foot fence post made of vinyl usually requires a "stiffener"—a metal insert—if it's being used as a gate post or an end post. Without that internal skeleton, the vinyl will flex under the weight of the gate, and eventually, the latch won't line up anymore. It’s annoying. You’ll be out there every morning lifting the gate just to get it to click shut.
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Common pitfalls with 6-foot heights
If you are specifically using these for a 4-foot fence, check your local utility lines first. Call 811. It’s free. I once saw a guy hit a secondary power line because he thought "it’s just a shallow fence." It wasn't pretty.
Also, consider the "nominal" vs "actual" sizing. A 4x4 isn't 4 inches. If you’re building a custom gate and your math is based on a true 4-inch width, your gate won't fit. Always measure the actual physical 6 foot fence post you have in your driveway before you start cutting your rails.
Wind and Privacy
If you live in a high-wind area (like the Great Plains or coastal regions), even a 4-foot fence on 6-foot posts needs extra care. Use "shadowbox" styling where pickets are staggered on both sides. This allows air to flow through the fence rather than hitting it like a brick wall. It takes more lumber, but it saves the posts from snapping during a heavy gale.
If you’re dead set on a solid privacy screen and you only have 6 foot fence post materials available, you’re basically limited to a very short fence. Don't try to cheat the system by only burying the post 12 inches deep. The leverage of a 5-foot-high fence on a 12-inch deep post is a recipe for disaster. One good push and it's over.
Actionable steps for your project
Before you head to the lumber yard, do these three things:
- Measure your total linear footage and divide by 8. Most fence panels are 8 feet wide, so you'll need a post every 8 feet plus one for the end.
- Check your local frost line. Google "frost line depth + [your county]". If your frost line is 24 inches, a 6 foot fence post is the absolute minimum you can use for a 4-foot fence.
- Select your hardware. Buy high-quality, ceramic-coated or stainless steel screws. Standard zinc screws will react with the chemicals in pressure-treated wood and corrode within a year, leaving ugly black streaks running down your beautiful new fence.
Pick up a "post level"—it’s a cheap plastic tool that straps to the post and shows you if you’re level on two sides at once. It’s way better than trying to hold a standard level while also pouring concrete.
Once your posts are in, let the concrete cure for at least 24 to 48 hours before you start nailing rails to them. If you start hammering on "green" concrete, you'll vibrate the post and create a tiny gap between the wood and the concrete. That gap will fill with water, freeze, and eventually ruin the stability of the entire line. Patience is the hardest part of the job, but it’s what separates a fence that lasts 20 years from one that leans after two.