Even SpacingHow to space balusters evenly
Pick the gap you want, then find how many balusters fill the opening with equal gaps. Do not space by eye and do not nudge the last baluster to make it fit.
Worked example
A length of 48 in needs 9 balusters with gaps of 3.45 in.
(48 − 9 × 1.5) ÷ 10 = 3.45 in
Try your own length
9 balusters, with gaps of 3.45 in.
(48 − 9 × 1.5) ÷ 10 = 3.45 in
Center each baluster at these distances from the start:
- Mark 1: 4.2 in
- Mark 2: 9.15 in
- Mark 3: 14.1 in
No fit. At this length the balusters cannot sit with gaps of 3.875 in or less. Try a longer length.
Type a length in inches, for example 48 or 48.5.
The method
- Measure the opening between the two posts, in inches.
- Pick the widest gap you allow. For a guard, this is the 4 inch rule below.
- Find the smallest number of balusters whose gaps are no wider than that.
- Divide what is left after the balusters by the number of gaps. A gap sits against each post, so there is one more gap than balusters.
The 4 inch rule
The International Residential Code requires that a guard does not let a 4 inch sphere pass through. The rule is IRC 2024 R321.1.3. In the 2021 edition and earlier it is R312.1.3. Your local code may differ, so check with your building department.
This page uses a widest gap of 3 7/8 inches, which leaves 1/8 inch of margin under the sphere. The balusters are 1.5 inches wide, the size of a 2x2.