Baluster Calculator

A baluster is a vertical member in a railing. This tool lays out equal-width members along one straight measured span. It assumes the outside edges of the first and last baluster are flush with the ends of that span.

Enter the minimum and maximum clear gap you want between adjacent baluster edges. These are project inputs, not values selected by the calculator. The first and last balusters touch the measured ends, so the model has no end gaps. If your end posts need openings, measure and assess those separately.

For example, a 10 in span with two 2 in balusters has one 6 in clear gap and 8 in center-to-center spacing. With a 4–6 in entered gap range, this is a valid arithmetic layout.

For span L, member width W, and integer count n of at least two, the clear gap is (L − n × W) ÷ (n − 1). Center spacing is that gap plus W. The calculator chooses the fewest members that keep the clear gap at or below your maximum, then checks your minimum and whether all members fit.

For a 96 in span, 2 in members, and a 4–6 in clear-gap range, 13 members leave 70 in for 12 gaps: 5.83 in clear and 7.83 in center-to-center. Twelve members would leave 72 in over 11 gaps, or 6.55 in, above the entered maximum.

The 2024 International Building Code §1015.4 describes a 4 in sphere opening test for many required guards and lists exceptions. That is an example of a specific code provision, not a universal gap input. This calculator does not test the full guard, loading, height, or local adoption. Source edition: 2024; source checked 2026-09-29.

Measure the available straight span at the baluster location and the actual width at the opening. Mark the two flush end positions and distribute the remaining positions by the calculated center spacing. Recheck the physical clear openings after installation, including openings near posts and below rails.