Spindle (Baluster) Spacing Calculator
Construction & Home ImprovementCalculate the minimum number of spindles and the resulting even spacing for a railing, kept within the IRC 4-inch maximum gap rule.
Spindles Needed
Minimum number of spindles needed so no gap exceeds the maximum allowed spacing.
Actual Even Spacing
4.000
Actual gap between spindles once evenly spaced with this many spindles.
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Creators
Odeh Ahwal0people find this calculator helpful
Views
Helpful
Saved
Embeds
Construction & Home Improvement calculators
Frequently Asked Questions
Where does the 4-inch maximum come from?
The International Residential Code, Section R312.1.3, requires that a 4-inch sphere cannot pass through any opening in a guardrail or stair railing, a safety rule intended to prevent young children from slipping through or getting their head stuck. Most local codes in the US follow this same limit, but always confirm your local code, since some jurisdictions vary.
Why round up to a whole number of spindles?
A fractional spindle cannot be installed, so the calculated minimum is rounded up to the next whole spindle. Rounding up, rather than down, guarantees the resulting even spacing never exceeds the maximum allowed gap.
Can I use a smaller maximum spacing than 4 inches?
Yes, some decks or commercial applications use a stricter limit, such as for pool safety fencing. Adjust the maximum allowed spacing field to any value your specific code or design requires.
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