A baluster layout must distinguish the opening being filled, the actual member width, the clear space between members, and the running marks used for installation.
Use the baluster spacing calculator
Define the opening and mounting condition
For an inside-mounted layout, measure the clear distance between the faces that bound the infill. For a face-mounted layout, define the usable rail length and any end offsets. Do not mix outside post dimensions with a clear opening.
Measure every bay: Nominally equal railing sections may differ enough to require separate layouts.
Use actual baluster width
Measure the installed face width of the baluster in the direction of the gap. Nominal material names, turned profiles, and angled stair intersections can differ from the effective width used in the spacing equation.
Choose the count from a gap limit
When a maximum desired clear gap controls, increase the whole baluster count until the calculated exact gap is at or below that selected limit. The calculator distributes the remainder evenly rather than leaving one odd end gap.
Code caution: A selected gap limit is not automatic jurisdiction-specific approval. Confirm the complete guard and stair requirements locally.
Mark running positions
Use cumulative centerline or edge marks from one verified reference face. Running measurements avoid repeatedly adding a rounded gap, which can accumulate error across a long rail.
- Confirm the first reference face
- Mark centers or one consistent edge—not a mixture
- Check the final mark before fastening
- Use a story pole or spacer block only after the math is verified
- For stairs, keep the selected measurement direction consistent
Check the entire guard assembly
Baluster spacing alone does not evaluate guard height, handrails, post attachment, loads, openings at stairs, climbability provisions, material systems, or structural connections.
Sources and review
Last reviewed July 26, 2026. The associated calculator includes tested fixtures, explicit assumptions, and input validation.
Field conditions, product instructions, approved plans, and applicable local requirements control the actual project. Review the full measurement disclaimer.