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Baluster Spacing Calculator

Estimate baluster count and even on-center spacing.

Baluster spacing must leave no gap a 4 inch sphere can pass through, so on-center spacing is typically 4 inches plus the baluster width — about 5.5 inches for a 1.5 inch baluster. Divide the clear run between posts by that spacing, round up and add one. Enter your rail length for exact baluster count and even spacing.

How does the baluster spacing calculator work?

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.

Which guide explains this in more depth?

Riser-and-tread math plus 2026 material prices for a full stair build. Read the stair calculator cost breakdown guide for the full worked example.

What else do people ask about this calculator?

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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