How Equal Spacing Is Calculated
Whether you're installing deck balusters, fence pickets, shelf brackets, or tiles, knowing the exact spacing before you start prevents costly mistakes. The calculation depends on whether the end items sit at the very edges (ends included) or whether items are placed inside a span (ends excluded). Ends included: spacing = usable length รท (n โ 1). Ends excluded: spacing = usable length รท (n + 1).
IRC building code requires baluster spacing to be no more than 4 inches to prevent a 4-inch sphere from passing through โ a child safety requirement. Use this calculator to find the minimum number of balusters needed: keep increasing the count until the spacing drops to 4 inches or less. The individual position list shows where to mark your chalk line for each piece.
For tile layouts, set the margin to accommodate edge cuts or grout borders. The position output represents center points of each tile. If you need gap-to-gap spacing rather than center-to-center, subtract the tile width from the spacing result. Always double-check positions with a dry layout before cutting or fastening.
Frequently Asked Questions
Ends excluded means items are placed entirely within the span โ none of them sit at the very start or end. There are n items and n+1 gaps. Example: 3 balusters between two posts create 4 equal gaps (margin + gap + b + gap + b + gap + b + gap + margin).
Yes. The calculator works with any unit. Just use the same unit for total length and margin. The spacing and position results will be in that same unit.
Round to the nearest 1/16 inch or 1 mm. Accumulate rounding error at the end or center of the span โ that's where it's least visible. A laser level or story pole helps keep marks accurate across a long run.