How this instrument works
A fence isn't held up by rails and pickets alone — everything ultimately hangs off a line of posts set into the ground at regular intervals. The distance between posts, called the spacing, is a design and structural choice: tighter spacing means a sturdier fence and more material, while wider spacing saves on posts but asks each section of rail to span further unsupported.
Dividing the total fence length by the chosen post spacing gives the number of sections between posts, and because a fence can't be built with a fractional section, that division is rounded up to the next whole section. The post count itself is always one more than the section count — a straight run of N sections needs a post at the start, a post at the end, and a post at every point in between, which works out to N+1 posts total.
This calculator covers one straight run of fence at a time. A fence line with corners, gate openings, or a mix of post spacings along its length needs to be broken into separate straight sections, each measured and calculated on its own, with the post counts added together — corner and gate posts also typically get shared between adjoining sections rather than double-counted.
- Enter Total fence length (ft) — the full straight-line distance the posts need to span.
- Enter Post spacing (ft) — the on-center distance between posts, 8 ft by default, a common wood-fence spacing.
- Read Posts needed — the fence length divided by spacing, rounded up to a whole section, plus one extra post for the run's starting end.
- For a fence with corners or gates, calculate each straight section separately and add the post counts together, sharing any post that sits at a shared corner or gate opening.
Worked example — a 100 ft fence at 8 ft spacing
Enter 100 into Total fence length (ft) and 8 into Post spacing (ft) — a common residential fence run with standard 8 ft post spacing. Dividing gives 100 ÷ 8 = 12.5 sections, and since a fence can't have half a section, that rounds up to 13 full sections.
Posts needed reads 14 — the 13 sections plus one extra post to close out both ends of the run. That's one post every 8 ft along the fence, with the last section coming in slightly under 8 ft to make the total length work out evenly.
Questions
Why is the post count always one more than the section count?
Because posts sit at the boundaries between sections, not in their middle — a single section of fence needs a post at each end, which is 2 posts for 1 section, and every additional section only adds one new post since it shares a post with its neighbor. Generalizing that pattern, N sections always need N+1 posts, which is exactly the +1 this calculator adds after rounding up the section count.
Why does the section count round up instead of to the nearest whole number?
Because a fence physically can't end partway through a section — if the raw division works out to 12.5 sections, the extra half-section of run still needs a full post-to-post section (and its post) to close out the fence, even if the last section ends up shorter than the standard spacing. Rounding down would leave the fence physically short of its target length, so this calculator always rounds up.
What post spacing should I use?
8 ft on-center is a common default for standard wood picket and privacy fencing, but real spacing varies by fence height, material, and local wind or frost conditions — taller privacy fences and heavier materials often use tighter 6 ft spacing for extra rigidity, while lighter field or wire fencing can go wider. Check your fence system's manufacturer guidance or a local fence contractor for the spacing appropriate to your specific fence type.
Does this account for corner posts or gate posts separately?
Not directly — this calculator finds the post count for one continuous straight run only. A fence line with corners or gates needs to be measured and calculated as separate straight sections, with the individual post totals added together; a post that sits exactly at a shared corner or gate opening is typically shared between the two adjoining sections rather than counted twice, so subtract one from the combined total for each such shared post.
How is this different from the fence materials calculator?
This instrument answers only the posts-needed question for a straight fence run. A fuller fence-materials calculation adds rails, pickets, and post-hole concrete on top of the same post count this tool produces, useful once you're ready to build a complete shopping list rather than just checking how many posts a run requires.