How this instrument works
A picket fence is built from a row of narrow vertical boards, or pickets, fastened to horizontal rails with a consistent gap left between each one. That gap is a design choice as much as a structural one: a narrow gap or none at all (a 'shadowbox' or privacy style) blocks sightlines almost completely, while a wider gap saves on materials, lets more light and air through, and reads as more open and decorative.
The distance from the start of one picket to the start of the next — its pitch — is simply the picket's width plus the gap you're leaving. Dividing the total fence length by this pitch tells you how many pickets are needed, and because a picket fence can't be built with a fractional picket at the end of a run, the instrument rounds that division up to the next whole picket.
This calculation covers one straight run of fence at a time. A fence line with corners, gate openings or varying picket spacing along its length needs breaking into separate straight sections, each measured and run through this instrument on its own, with the individual picket counts added together for the full job.
- Enter Fence length (ft) — the total straight-line distance the pickets need to cover.
- Enter Picket width (in), the width of a single picket board, 5.5 in by default.
- Enter Gap between pickets (in) — the spacing you're leaving between neighbouring pickets, 0.25 in by default.
- Read Pickets needed — always rounded up, since a picket fence can't end on a fractional picket.
- Run the calculation separately for each straight section between corners or gate openings, then add the picket counts together for the full fence.
Worked example — a 50 ft run, 5.5 in pickets, 0.25 in gap
Enter 50 into Fence length (ft), 5.5 into Picket width (in) and 0.25 into Gap between pickets (in) — a 50 ft picket fence run with a modest quarter-inch gap between boards. Fifty feet converts to 600 in, and picket pitch is 5.5 + 0.25 = 5.75 in.
Dividing 600 by 5.75 gives 104.35, and Pickets needed rounds that up to 105 — 104 full-pitch pickets plus one more to close out the remaining 0.35 of a picket's worth of run, since a fence can't stop partway through a picket.
Questions
Why does the picket count always round up?
Because a fence run can't literally end on a fraction of a picket — if the raw division works out to 104.35 pickets, that extra 0.35 still requires a whole 105th picket physically present (even if trimmed) to close out the run cleanly. Rounding down would leave a gap wider than intended at the end of the fence, so the instrument always rounds up rather than to the nearest whole number.
How does the gap I choose affect privacy and picket count?
A wider gap means fewer pickets cover the same fence length, since each picket-plus-gap pitch gets larger — but a wider gap also opens up more sightline through the fence, trading privacy for material savings. A tight gap or a butted 'shadowbox' style (effectively a gap near zero) maximizes privacy at the cost of needing close to one picket per picket-width of fence length.
Does this account for corner posts, gate openings or end posts?
No — this instrument covers only the picket count for one continuous straight run of the given length. Corner posts, gate openings and end posts are separate structural elements planned outside this calculation; for a fence with corners or gates, measure and calculate each straight section between those features separately, then add the picket totals together.
Should I buy extra pickets beyond the calculated count?
Yes, a small buffer is standard practice — many installers add a handful of extra pickets, or roughly 5%, to cover any that split, warp or are cut wrong during installation, and to have a matching replacement on hand if one is damaged later. The calculated figure is the minimum needed to physically close the run, not a materials order with waste built in.
Is this the same math used for deck board spacing?
Yes, structurally — both calculations divide a total run by a pitch (item width plus gap) and round up, because both problems are 'how many evenly spaced items close out this distance'. The real-world context differs: here it's vertical pickets spanning a fence's horizontal length, while a deck-board calculation spans a deck's width with horizontal boards — different objects, same underlying arithmetic.