Baluster Spacing Calculator

Post spacingrails

How to measure

Measure the clear space between the faces of two railing posts.

Section
Balusters

Must stay under 4 in. Many builders aim for about 3.5 in to leave room for wood shrinking.

Balusters per section

14 balusters

Gap of 3 3/8 in between balusters; 14 balusters for 1 section

How the estimate was calculated
Balusters per section14 balusters
Exact gap3.400 in
Gap to the nearest 1/16 in3 3/8 in
On-center spacing4 7/8 in
Gaps per section15
Sections1
Total balusters14 balusters

Assumes equal gaps between every baluster and at both posts. Mark the first baluster 3 3/8 in from the post, then every 4 7/8 in on center. The gap is under 4 in, so a 4 in sphere cannot pass between balusters.

See the formula, sources and worked examples on Matholio