Fence post calculator
Give it the run, the spacing you want and how many corners and gates there are, and it returns the post count broken out by type — because line, corner and gate posts are different purchases in different holes, and counting them as one number is how material orders come up short.
Actual bay width is the run divided evenly, so no bay is wider than your chosen spacing. Gate, corner and end posts want a bigger section and a deeper hole than line posts.
Why the bays come out under your spacing
A 100-foot run at 8-foot spacing does not give twelve 8-foot bays and a 4-foot stub. It gives thirteen bays of about 7'-8" each, because the run is divided evenly so that no bay exceeds the maximum.
That matters twice. It keeps every rail within its safe span — the reason there is a maximum at all. And it means your rail stock has to suit the real bay, not the nominal one, so pre-cut panels sized to a round number will not fit without ripping.
Three kinds of post, three different orders
Line posts are pulled equally in both directions by the rails, so the forces mostly cancel. They are the standard section in the standard hole.
End and corner posts are pulled from one side only. They want a heavier section, a bigger hole and often more depth — and on a long run they are frequently braced back to the next line post.
Gate posts carry a swinging cantilever that gets slammed and leaned on. They are the posts that fail, and they should be the biggest and deepest on the fence — see post depth and gate hardware.
Spacing is a real trade
Wider spacing means fewer posts, fewer holes and fewer bags of concrete — and it lands straight on the per-foot price, because the post is a fixed cost spread over the bay.
It also means longer rail spans, more sag over time, and more wind load on each post. Six-foot bays are the conservative choice for a tall privacy fence; eight is standard; ten wants the rail stock and the post section to justify it. Pick the spacing for the fence, then let the price follow — the reverse is how fences end up sagging.
Sources
Nothing here is asserted as a current figure. The tool is arithmetic on what you type, and every default is a round placeholder for your yard's quote.