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Baluster Spacing Calculator
Estimate baluster count and even on-center spacing.
How the baluster spacing calculator works
Building code requires that a 4 in sphere cannot pass between balusters. Compute balusters so gap = (rail length − n × baluster width) ÷ (n + 1) ≤ 4 in, then round up.
Frequently asked questions
How far apart should deck balusters be?
No more than 4 in clear gap between balusters — the '4 in sphere' rule required by IRC R312.
How do I center balusters?
Compute on-center spacing = baluster width + gap. Layout on-center from the first post, working outward.
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