Fence Post Calculator: How Many Posts, How Far Apart, How Deep

The spacing you choose is a maximum, not a target: the calculator divides each run into equal bays no wider than it. Panel and rail systems are the exception — there the panel is the spacing, so each run ends in one cut panel instead.

• Wood privacy: 8 ft at most, 6 ft when it's tall or windy. Rails and pre-built panels come in 8 ft lengths and a rail has to land on a post. The Home Depot wood-kit instructions also set end, corner and gate posts at least 6 in deeper — the calculator does the same.
• Vinyl: the panel width, 6′ or 8′ centre to centre. A vinyl panel can be cut shorter but never stretched, so the bay that doesn't fit is a cut panel, not a wider gap.
• Chain link: 10 ft maximum, spaced equally. ASTM F567 §4.1 spaces line posts “equidistant at intervals not exceeding 10 ft”, and §4.2 puts a terminal post at every end, corner and gate. A 145 ft run is 15 equal bays of 9′ 8″ on 16 posts — not 14 bays of 10 ft and a 5 ft stub.
• Wire on T-posts: 12–16 ft. University of Tennessee Extension recommends 12–14 ft for barbed wire and 14–16 ft for woven wire on flat ground; NRCS Illinois caps standard woven wire at 15 ft and barbed wire at 20 ft without stays. Every corner, end, gate and pull post is a braced wood assembly, not a T-post.

Fence posts are the textbook fence-post problem: a straight run cut into n sections needs n + 1 posts, because both ends need one. Everything else is bookkeeping about which posts are shared:

• Sections = run length ÷ maximum spacing, rounded up. A 100 ft run at 8 ft is 13 sections, so 14 posts.
• Corners are counted once. Two 40 ft sides counted separately come to 12 posts; joined at a corner they need 11, because the corner post serves both.
• A closed perimeter has no end posts. A square with 50 ft sides needs 28 posts — one per section, the four corners included.
• Each gate takes the opening out of the fence and adds two gate posts. The two pieces either side of it are separate runs, each rounded up on its own.

Worked example — the default in the calculator: a back yard of 50, 100 and 50 ft that stops at the house, with a 4 ft gate in the back side. That is 26 sections and 28 posts: 22 line, 2 corner, 2 end and 2 gate posts, set 7′ 1¾″ to 8′ apart.

This is the whole question for most people, so here it is in full rather than locked inside the calculator. A closed perimeter returns to where it started, so every section shares its posts. An open run — one fence line with two ends — needs one extra post to finish it.

Read each cell as closed perimeter / open run. Add one post per gate opening on top, and remember the gate width itself carries no panels.

The post you buy is the fence height plus whatever goes in the ground, and this is where the standard advice quietly fails. A six-foot fence is not an eight-foot post job in most of the country — it's eight and a half feet before the frost line is even considered, which is why so many fences end up with 24-inch footings they were never meant to have.

Local rules vary. Frost depth is set by your building department, not by a rule of thumb, and it overrides everything in this table. It ranges from nothing in the far south to four feet or more up north — look up the frost line for your zip code→, and see how deep fence posts should be→ for why a footing above it gets lifted every winter.

Concrete is the item people most often under-buy, because the intuition is about the hole and the arithmetic is about the hole minus the post. These figures already subtract the post and add 10% for the fact that a dug hole is never a true cylinder.

Bag counts are per post, so multiply by your post count and round up — you cannot buy a tenth of a bag, and having one spare is far better than stopping mid-pour. Setting posts in gravel instead of concrete→ is a legitimate alternative that drains better and makes future replacement much easier.

A quantity calculator is geometry, and geometry has limits worth naming:

• It can't size a gate post. A gate applies a swinging, twisting load no line post ever sees. Set gate and corner posts deeper and wider than the table says, and step up a post size if the gate is wide or heavy.
• It places gates mid-side. Gates are spread evenly along the side you put them on. Moving one toward a corner can shift the count by a post either way, so treat the run-by-run layout as a plan to check on the ground with a string line.
• Every join is a real corner. A slight bend doesn't need a corner post (NRCS only braces direction changes over 20°); enter a gentle curve as one side.
• It doesn't know your ground. Rock, roots and sand all change what the hole can actually be — see fencing on a slope→ for how grade changes the layout too.
• It isn't a permit check. Height caps, setbacks and pool-barrier rules are jurisdictional. Start at fence rules→ before you buy anything.

Call 811 before you dig, every time and everywhere in the US. It's free, it's usually required by law, and hitting a buried line is the one fencing mistake that can be genuinely dangerous rather than merely expensive.