Baluster spacing calculator
Calculate equal baluster spacing with code-compliant maximum gap. IRC requires that a 4" sphere cannot pass between balusters.
in
8.0 ftin
1.5" for 2x2in
4" IRC sphere rulein
3.5" for 4x4Railing layout
3-23/32″ gap — OK
Balusters needed
17
18 gaps
Actual gap
3-23/32″
3.7222″
On-center spacing
5-7/32″
5.2222″
Clear span
92-1/2″
Between post faces
Baluster Spacing Code Requirements
The IRC requires that a 4-inch sphere cannot pass through any opening in a guard or railing (IRC R312.1.3). This means the clear gap between balusters must be less than 4 inches.
The calculator finds the number of balusters needed to keep gaps under the maximum, then calculates the actual equal spacing. The result is always slightly under the max gap — ensuring code compliance while keeping the spacing as even as possible.
Do I include the post in the baluster count?
No. Posts are structural and separate from balusters. Enter the total railing length (post face to post face) and the calculator determines how many balusters fit between them.
These calculators are provided for estimation and educational purposes only. Always verify with your local building code.