Guard Baluster / Picket Count (4-in Sphere Rule)
Balusters on a guard or fence spaced so a 4 in sphere cannot pass: pickets = ceil((clear span - max gap) / (picket width + max gap)); actual gap = (clear span - pickets x width) / (pickets + 1). A 96 in span with 1.5 in pickets holds 17 pickets at a 3.92 in gap; 3.5 in wide pickets take 13 at 3.61 in. The clear span and picket width both drive the count. The guard height and load are checked by guard-handrail-check.
Formula and source
pickets = ceil((rail_clear_in - max_gap_in) / (picket_width_in + max_gap_in)); gaps = pickets + 1; actual_gap_in = (rail_clear_in - pickets x picket_width_in) / gaps.
Guard baluster spacing by name (the IRC 4 in sphere rule); first-principles equal-spacing arithmetic.
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