Baluster Calculator

Find how many balusters each railing section needs so no gap is wider than code allows, and the exact spacing to lay them out.

Codes require that a 4 in sphere cannot pass through; 3-7/8 in leaves a margin.

Balusters needed

52

  • Balusters per section13
  • Actual gap3.75 in
  • On-center spacing5.25 in

Estimates only. Round up when you order, and confirm structural details with your local building code.

How to use it

  1. Enter the distance between posts.
  2. Enter the number of sections.
  3. Enter baluster width and the maximum gap.

The formula

Balusters = (length − gap) ÷ (baluster width + gap), rounded up

Actual gap = (length − balusters × width) ÷ (balusters + 1)

Worked example

Railing length between posts72 in
Number of sections4
Baluster width1.5 in
Maximum gap3.875 in

Result

Balusters needed52
Balusters per section13
Actual gap3.75 in
On-center spacing5.25 in

Tips before you order

  • The IRC requires that a 4 in sphere cannot pass between balusters.

Questions

How many balusters for a 6 ft section?

With 1.5 in balusters and a 3⅞ in max gap: 13 balusters.