How Far Apart Should Fence Posts Be? 8 Feet Apart, 2 Feet Deep, and 2 to 3 Bags of Concrete per Post

Short answer: set fence posts 8 feet apart, on center, for a standard 6 foot wood fence, 6 feet apart for fences over 6 feet tall or horizontal designs, and up to 10 feet apart for chain link. Dig each hole 3 times the width of the post and deep enough to bury one third to one half of the post's above-ground height, with 2 feet as the minimum. A 4x4 post in a 12 inch hole 30 inches deep takes about 3 bags of 80 lb concrete over a 6 inch gravel base.

Those three numbers, spacing, depth, and concrete, decide whether a fence is still straight in 15 years or leaning in 5. At Gorilla Works the post is the part of a cedar fence we spend the most care on, because it is the one part you cannot fix later without rebuilding. Here is the math behind each number, and what changes in Portland's wet clay.

The 3 numbers at a glance

How far apart should fence posts be?

8 feet on center is the standard for a solid wood, vinyl, or composite fence, and it is not an accident. Fence rails come in 8 and 16 foot lengths, and pre-built panels come 8 feet wide, so 8 foot spacing means no waste and a rail joint on every post. Go to 6 feet when the fence is taller than 6 feet, when the boards run horizontal, or when the fence line takes wind off open ground, because a solid fence is a sail and the post spacing is what holds the sail up. Chain link can stretch to 10 feet because the mesh lets wind through, though the top rail starts to sag at that distance and 8 feet looks better.

• Measure on center, from the middle of one post to the middle of the next, not from edge to edge.
• Lay the run out from the corners and gates in, so any odd short section lands mid-run instead of at a gate.
• Horizontal fences are the exception to everything above. Long boards sag between posts, so 6 feet is the practical maximum and the board grade matters as much as the spacing.

How deep should a fence post be?

Bury one third to one half of the height that shows above ground, and never less than 24 inches. For a 6 foot fence that means an 8 foot post with 24 to 36 inches in the ground. Corner posts, end posts, and gate posts carry more load and go at the deep end of that range or deeper. The frost line is the other rule, and in the Portland area it is not the one that governs: the residential code frost depth for Portland and for Clark County, Washington is 12 inches, so the 24 inch minimum for holding the fence up is already well below it.

How much concrete per fence post?

About 2 to 3 bags of 80 lb concrete for a 4x4 post in a 12 inch hole, depending on depth. The math is simple: the volume of the hole, minus the volume of the post inside it, divided by what one bag makes. An 80 lb bag of fast-setting mix yields 0.60 cubic feet, a 60 lb bag 0.45, and a 50 lb bag 0.375. The table below assumes 6 inches of gravel at the bottom of the hole, which is standard, so the concrete column is 6 inches shorter than the hole, and it rounds up to whole bags because you cannot buy half of one.

Buy 10 percent extra. Holes are never perfectly round, clay walls slump, and the last post always needs a little more than the first. A 100 foot fence at 8 foot spacing has 13 or 14 posts, so at 3 bags each you are hauling about 40 bags of 80 lb mix. That weight is one reason crews pour from a mixer instead of by the bag on long runs.

How do you set a fence post so it stays straight?

• Dig the hole 3 times the post width and to the depth in the table, with straight sides. A bell-shaped bottom, slightly wider than the top, locks the footing in against frost heave and pull-out.
• Drop 6 inches of gravel in the bottom and tamp it. The post sits on gravel, not on concrete, so water that runs down the post can drain instead of pooling at the end grain.
• Set the post, brace it plumb in both directions, and check the spacing to the last post one more time.
• Pour fast-setting mix dry around the post to 3 to 4 inches below grade and add about a gallon of water per 50 lb bag, or mix wet first for a stronger footing. It sets hard in 20 to 40 minutes.
• Crown the top of the concrete so it slopes away from the post, then bring soil or gravel back up over it. Concrete that cups toward the post holds water against the wood and rots it at the ground line, which is where most wood posts fail.
• Wait about 4 hours before hanging rails or putting any load on the post, and longer before hanging a gate.

What changes in Portland's wet clay?

Most of the Portland metro sits on clay that holds water for nine months a year. Clay does two things to a fence post: it keeps the base of the post wet, which is what rots pressure-treated wood, and it swells and shrinks with the seasons, which is what walks a shallow post out of plumb. The fixes are the ones above, done without shortcuts: the full depth, the gravel base under the post, the crowned concrete cap, and a kickboard along the bottom of the fence so the cedar boards never touch wet ground. The other fix is to take wood out of the ground altogether.

That is why we offer galvanized steel posts on cedar fences. The post never rots, it can be wrapped in matching cedar so the fence still reads as wood from both sides, and it is the one upgrade that changes how long the whole fence lasts rather than how it looks.

Frequently Asked Questions

Can fence posts be 10 feet apart?

For chain link, yes. For a solid wood or vinyl fence, no. At 10 feet the rails sag, the boards wave, and the fence catches more wind than the posts can hold. 8 feet is the maximum for a solid fence and 6 feet is better for anything tall or horizontal.

Is 2 feet deep enough for a fence post?

For a 4 foot fence, yes. For a 6 foot fence, 2 feet is the minimum and 30 inches is the safer number, especially in soft or wet soil. Gate posts always go deeper than the line posts.

Do fence posts need concrete?

For a solid fence in the Portland area, yes. Gravel-only settings work for split rail and farm fencing where wind load is low and the post can be reset easily. A 6 foot privacy fence on wet clay needs the concrete to hold it plumb through the seasons.

Should the post sit in the concrete or on gravel?

On gravel, with concrete around it. If the bottom of the post is sealed inside concrete, water that runs down the post has nowhere to go and the end grain sits wet. Six inches of gravel under the post lets it drain.

How long before you can hang a gate on a new post?

Fast-setting mix sets hard in under an hour and takes light load in about 4 hours, but a gate is a lever on the post, so give a gate post at least a day, and use a 6x6 post in an 18 inch hole for any gate wider than 4 feet.

How many fence posts do I need for 100 feet of fence?

At 8 foot spacing, 100 feet of straight run needs 13 posts plus one at the end, so 14, and every corner or gate adds one. At 6 foot spacing it is 17 or 18.

The bottom line

8 feet apart, at least 2 feet deep in a hole 3 times the post width, 6 inches of gravel under the post, and 2 to 3 bags of 80 lb concrete crowned away from the wood. Get those right and the fence stays straight for as long as the boards last. Skip one and the post is the first thing to go.

If you would rather have the digging, the depth, and the concrete on someone else's shoulders, our fence installation team sets every post to these numbers or better.

Planning the rest of the fence? Read our guides on Portland and Vancouver fence height and property line rules and on the different types of fences before the first hole goes in.

Gorilla Works proudly serves Portland, Gresham, Beaverton, Hillsboro, Tigard, Lake Oswego, Happy Valley, Milwaukie, Troutdale, Vancouver WA, and Camas WA. Call (971) 343-4964 or request a free fence quote.