Wood posts are the ones to carry the most of the fence weight so they should be larger than the panels and the railings. You should choose post materials with a 4 inch width and 4 inch thickness, giving you square wooden board for you post.
Wooden Fences. If you're using ready-made fence panels, post spacing is already determined. If you're building your own fence using individual fence boards, choose a distance between 5 and 8 feet.
This way you will have even spacing between the fence post for people who can see it to view. Then you probably will have to trim your "header" boards, as you described, to fit between them a little tight to begin with. ... Wood posts usually die before the fence. Metal posts will outlive the wood fence and allow for easy (relatively) refencing ...
Most wood fences are spaced 8 feet between fence posts. This isn't for a structural purpose, although 8 feet provides enough support for a wooden fence. Dimensional lumber is usually available in 8 or 16 feet lengths, so having posts 8 feet apart means less cutting and wood waste.
Most wood fence is constructed with post spacing of 8' on centers. The reason is that most dimensional lumber is available in 8' or 16' lengths. Also spacing of more than 8' will likely result in sagging of the rails. You can space posts closer together if desired, but try to use a space that will result in minimum waste of lumber.
Install a bottom and top rail to attach to the fence posts. In this project, we used a "butt joint" to secure the rail to the body of the post rather than the top of the post. A "butt joint" is a basic wood joint where the ends of the rails are aligned, placed together and then secured.
Line Posts: Line posts support the material intermittently along the length of each side of the fence and can be either steel t-posts or wooden posts. When selecting posts, be sure that the posts are at least 3" taller than the fence they are supporting.
Fence Material and Post Centers Calculator To estimate the amount of fence posts, rails, pickets, and hardware you need, enter your fence length, number of rails, and picket dimensions. You’ll also get a cost estimate for pressure treated wood, cedar, and redwood.
FIG. 1 - Space and dig the post holes every 6' to 8' apart.: SPACING THE FENCE POSTS. As a rule, you should set fence posts about 6' to 8' apart. The spacing of the posts depends on the type of fence you build, the terrain, the purpose of the fence and other such factors.
(Also, by spacing the posts 7.5 feet apart, you’re leaving some wiggle room to cut the rails to size in case a post isn’t perfectly centered in its hole or a measurement is slightly off.) For a fence with three rails, cut one rail in two and use one of the halves to start the middle-rail row.