Fence Picket Spacing Calculator

How to use it: enter the opening width between posts, the picket width, the picket height (used only to draw the diagram), and the largest gap you'll allow between pickets. The tool finds a symmetric layout - including the gaps at both ends - that keeps every gap at or under your maximum.

Formula. For n pickets there are always n + 1 gaps (one before the first picket, one after the last, and one between each pair), so the tool searches upward from n = 1 for the smallest picket count where the resulting gap is no larger than your maximum:

gap = (opening − n × picket width) ÷ (n + 1)

It stops at the first n where gap ≤ maximum gap (and gap is non-negative), then reports center-to-center spacing as picket width + gap.

Worked example. With the defaults above (2400 mm opening, 90 mm picket, 80 mm max gap): at n = 13 pickets, gap = (2400 − 13×90) ÷ 14 = 1230 ÷ 14 ≈ 87.9 mm, which exceeds 80 mm. At n = 14 pickets, gap = (2400 − 14×90) ÷ 15 = 1140 ÷ 15 = 76.0 mm, which fits - so the tool settles on 14 pickets, a 76 mm gap, and 90 + 76 = 166.0 mm center-to-center spacing.

The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.

Opening width

2400 mm

Picket width

90 mm

Picket height

900 mm

Maximum gap

80 mm

Primary result: Pickets: 14.

• Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
• Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
• When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.

The opening width you enter should be the real clear distance between posts (or other fixed boundaries) at installation, not a nominal or on-paper dimension - actual post positions, out-of-square framing, and timber that has swelled or shrunk will all shift real gaps slightly from this calculation.

The tool assumes a single row of identically sized pickets with uniform gaps and doesn't account for corner or end conditions that need a narrower picket, fasteners that take up space, or pickets installed at an angle (shadow-box or louvre styles).

Maximum-gap requirements for fences and railings are set by local building codes and vary by jurisdiction and application (pool fencing is typically stricter than a boundary fence) - treat any number you use here as something to verify locally, not a universal standard.