Fence material take-off

Sections, posts and the extra one at the end of every run

Sections come first: the run divided by the post spacing, rounded up, because a fence cannot end mid-air and a partial span still needs a whole panel’s worth of material. The exact, unrounded spans figure is reported beside the count, and the gap between the two is the short bay at the end of the walk — already paid for, worth knowing about before the panels are cut.

Posts are the sections plus the one that closes the line. It is the figure people undercount by exactly one when they order from memory, and it is the primary answer here because everything set in concrete flows from it.

Rails multiply the sections, and how many run through each section is a style decision the reader supplies: the default expresses a plain rail fence, and a taller or panelled design carries its own figure. The rail count never sees the posts — only the bays between them.

Concrete arrives as bags per post, another input rather than a rule: the default sets each post in a single bag, a heavier gate line earns more, and a driven or gravel-set run can enter none at all. The bag total simply repeats the post count that many times.

The post spacing itself is the reader’s to own. The default is the pack’s shipped figure; panel widths, wind exposure and gate positions all pull it around, and a bent line is better run leg by leg, because a corner interrupts the rhythm and restarts the count.

When this calculation is used

• Ordering posts, rails and post-set concrete once a boundary line is measured.
• Checking a fencing quote by setting its post count against the run and spacing it claims.
• Seeing how far the last bay falls short before deciding where to absorb the odd section.
• Costing the concrete line of a fence job by varying the bags set under each post.

Worked example

The pack’s golden vector: a run of one hundred feet at the default spacing, the default pair of rails in each section and a single bag under every post — beside a companion vector whose shorter run refuses to divide evenly, so the rounding has work to do.

In both vectors the post count sits exactly one above the section count — the closing post at the end of the walk — and with a single bag per post the concrete order simply repeats the post figure. In the companion vector the exact spans figure falls short of the rounded section count: that gap is the short final bay the order has already bought.

Each figure on this page is produced live by the certified engine and checked against the signed pack’s declared test vectors when the calculator loads; nothing here is a stored answer. Set the post spacing to zero and the engine refuses rather than divide by it — the pack declares that refusal as a vector.

What each input represents

Assumptions and limits

• The run is a single straight line; corners and gates interrupt the post rhythm, so a real boundary is entered leg by leg with its openings left out.
• Posts are counted as line posts with one closer at the end; gate posts, bracing and end hardware are additions the arithmetic does not see.
• Rails per section and bags per post are reader-supplied or pack-defaulted inputs describing a style and a setting method, never assertions about what a fence requires.
• The order counts members and bags only — pickets, panels, fasteners, gates and labour are separate lines.

What the guards protect against

• The post spacing must be strictly greater than zero, and the pack ships that refusal as a declared test vector: a spacing of nothing turns the section count into a division without meaning, so the engine refuses instead of planting infinite posts.
• The run must be strictly positive and is capped at a figure generous enough for a long field boundary but no further, so a unit slip is refused before it fences a county.
• Rails per section and bags per post may both be zero — a panel system with its own rails, or posts set without concrete — but each is bounded above, so a mistyped figure cannot silently multiply the order.

Provenance

Standard fence run take-off arithmetic (spans-plus-one convention)

Sections as the run over the post spacing rounded up; posts as one more than the sections; rails and concrete bags as per-section and per-post multiples; the exact spans figure reported unrounded alongside.

Quantity reference to be verified against the site and the products actually ordered; post embedment, wind loading and boundary positions are never determined here. The signed pack carries its own citation, and the page reports the verification state of the release it mounted.