What Size Posts for a Wood Fence?

Updated February 21, 2017

The posts of any fence are key to keeping the fence stable and sturdy. Wood fences commonly use wood posts as supports. The size of the posts varies with the height of the fence as well as some other factors. Knowing the design of the fence and some basic height dimensions helps choose the correct sized wood post for a wood fence.

Post Measurements

Wood posts used for fences can be either square or round. Square posts are milled to precise sizes and of uniform size while round posts have greater size variation. Round post sizes are given as the diameter of the top of the post, in inches, and the length of the post in feet. For Example, a 6-inch by 8-foot round post is 6 inches across the top end of the post and 8 feet long. A square post is stated as size, in inches, of each side of the post and then the length. A 4-by-4-post is 4 inches wide on each of its square sides. This would be followed with the length of the post in feet.

Minimum Heights

The post must reach as high as the top horizontal rail of the fence. In many fence designs the top horizontal rail is below the top of the fence. For example, a 6 foot high fence with the top rail 1 foot below the top of the fence must have posts that reach at least 5 feet above the ground.

Overall Post Length

Wood posts are commonly set so about one-third of the posts length is in the ground. For example, an 8-foot- long post would be buried about 2 feet 8 inches, leaving just over 5 feet of the post protruding above ground.

Post Size

Higher fences create more of a strain on the posts because they have a larger fence surface catching the wind. Fences less than 8 feet tall call for posts measuring 6 by 6 inches, according to the building codes of Livermore , Calif. Fences less than 10 feet tall can use 6-by-6-inch posts if the posts are placed every 5 feet along the fence line. Fences taller than 10 feet, or with posts placed more than every 5 feet, should utilise 6-by-8-inch posts.

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About the Author

Keith Allen, a 1979 graduate of Valley City State College, has worked at a variety of jobs including computer operator, medical clinic manager, radio talk show host and potato sorter. For over five years he has worked as a newspaper reporter and historic researcher. His works have appeared in regional newspapers in North Dakota and in "North Dakota Horizons" and "Cowboys and Indians" magazines.