Compare dimensions without treating them as a design approval
Six feet and eight feet are useful layout comparisons, but neither is a universal structural recommendation. The appropriate support interval depends on the actual fence system and site requirements. Obtain the permitted configuration from the relevant product instructions or project design before choosing a value. This planner then distributes the supplied maximum across your measured Runs. It does not infer adequate Post size, Rail strength, wind resistance, connections or footing depth from the number six or eight.
Start with the six-foot Bay preset and compare it with the eight-foot preset. Both retain the same default Runs, Gate and Corner, so the maximum Bay is the only deliberate change. Record the resulting Post count and actual Bay Clear Lengths for each. If you change the Run lengths at the same time, you will no longer be isolating the effect of the maximum interval. Save a separate URL for each candidate.
Identify what the spacing number measures
The EvenGap input is Maximum Bay clear length: the empty distance between the inside faces of neighboring Posts. It is not a center-to-center interval. With 3.5-inch Posts, a 96-inch clear opening corresponds to 99.5 inches between centers. An eight-foot center-to-center requirement would instead leave a 92.5-inch clear opening. Check the terminology in the product or design you are following before entering the value. A field name is part of the geometry, not merely a label beside a number.
A Run’s Overall Length is also a different measurement. It extends from the outside face of its first Post to the outside face of its last Post, so both terminal supports are included. The first center is half a Post width from that origin. If you already have a measured clear opening between two Posts, do not put that number into a Run Overall Length field and deduct the Posts again. For individual openings that only need infill, use a Bay-based spacing tool instead.
See how the maximum creates whole Bays
For a 40-foot Run, the Overall Length is 480 inches. With 3.5-inch terminal Posts, the provisional clear distance is 473 inches. At an eight-foot maximum, divide 473 by 96 and round up to five Bays. Five Bays require six Posts. Deduct all six Post widths from 480 and divide by five to obtain 91.8 inches clear per Bay. The resulting opening is shorter than the maximum because the Run needs a whole number of Bays and every intermediate Post occupies material.
At a six-foot maximum, divide the same 473 inches by 72 and round up to seven Bays. Seven Bays need eight Posts. Their widths consume 28 inches, leaving 452 inches divided among seven openings, about 64.571 inches each. The actual opening is not exactly six feet. The maximum limits the result; it does not force every interval to equal the requested number. The final outside face still lands at the original 480-inch boundary because the Post and Bay widths are accounted for together.
Compare the full default Plan
The default second Run is 24 feet, or 288 inches. At an eight-foot maximum it uses three Bays and four Posts, with each clear opening 91⅓ inches. At a six-foot maximum it uses four Bays and five Posts, with each clear opening 67.625 inches. The Gate reuses adjacent Posts, and the Corner shares a center rather than adding a duplicate support. Read the Plan’s actual Post count instead of adding independent Run counts without considering those shared boundaries.
The Gate width and hardware clearances stay unchanged in this comparison. The default four-foot leaf and two 3/8-inch allowances create a 48¾-inch opening. The interval change affects the interior Posts of the Runs, not the width of the Gate itself. In the drawing, check that the Gate and Corner retain their intended positions relative to the path. Their global distances can depend on the outside-face convention, so use the Post table and the annotated Runs together when relating the two candidates to your sketch.
More Bays change more than the Post count
Each added Bay creates another separate opening for the picket solver. The picket count is rounded within each Bay, not once across the whole fence. Consequently, changing the Post interval can change both the number of Posts and the total number of installed pickets. It also changes the solved Gaps slightly. If the total seems counterintuitive, open the Bay result table and compare one opening at a time. A global estimate based only on total length and pitch cannot explain those local changes.
Rail cuts also follow the Bays. With two Rails per Bay, the default eight-Bay Plan creates 16 cuts. A Plan with more Bays creates more, shorter cuts. This does not directly tell you which stock lengths are cheapest, because saw kerf, connection details and reusable offcuts affect that purchase. Copy the cut list into your buying worksheet and compare it with the stock actually available. Do not treat the number of cuts as an optimized count of store-bought long Rails.
Keep footing quantity inputs separate
The Post-only tool estimates concrete from your entered hole diameter, buried length, square Post width and bag yield. It models a cylindrical hole and subtracts the volume occupied by the Post. The example buried length and hole diameter are arithmetic inputs only; the planner does not decide that those dimensions are suitable. Obtain the required footing geometry independently, then enter it. A larger number of Posts usually changes the aggregate quantity even when every individual footing remains the same size.
Concrete is rounded up to a whole bag after the modeled volume is summed. The default bag options use approximate yields for the specified weights, which must be checked against the actual mix label. Irregular excavations, overdigging, different footing shapes and handling losses are not represented by a perfect cylinder. Record those differences before purchasing. A visible concrete count is useful only when the input geometry and product yield match the job; it should not imply that the tool has selected an acceptable footing design.
Use local center measurements for setting out
Open the Post-center table and identify the first Post for each Run. The local centers start half a Post width from that Run’s outside face. Measure each center from the same origin rather than stepping a rounded interval along the string line. The displayed fractions are rounded for readability, while the underlying coordinates remain unrounded. Repeatedly adding a rounded pitch can shift the far support even when every individual step looks reasonable. Compare the last center plus half a Post width with the measured Overall Length.
Before committing to a candidate, check the selected product’s permitted configuration, the actual stock dimensions and the Gate hardware requirements. Save the preferred URL, print the position table, and label its origin and Run order on your site sketch. If a support moves during installation, remeasure the affected opening and regenerate its infill layout. The calculation reference explains the formulas, while the Gate layout guide explains shared supports. Together they let you trace a quantity difference back to an explicit dimension instead of guessing why six feet and eight feet produced different totals.