Baluster Spacing Calculator — Verified Layout & Marks
Plan baluster counts and exact centre marks across one or more railing bays. Check every clear gap after rounding marks to your tape increment.
See the gap you will actually install
Widest clear gap: 3.75 in
1 bay · marks rounded independently to the nearest 0.0625 in from the left inside post face
Set your own maximum clear gap. This is a spacing plan, not a local code or structural approval.
Edit the layout ↓Plan your railing bays
Measure each clear opening between the inside faces of posts. Use the finished width of one baluster. Marks are centre lines measured from the left inside post face.
Clear openings
Enter inches with up to three decimal places, or tape fractions with denominators 2, 4, 8, 16, 32 or 64 (for example, 27 1/8). Up to 12 separate bays and 400 balusters per bay.
Your measured plan
13 balusters
72 in clear · widest installed gap 3.75 in
The fewest balusters fit after every centre mark is rounded to your chosen tape increment.
Centre marks from the left post
| Baluster | Centre mark | Left edge | Right edge | Gap before |
|---|
Final gap to the right inside post: 3.75 in
Check installed positions and product dimensions on site. Curved, sloping or raked runs need a layout measured along their own geometry. Posts, rails, fasteners and structural suitability are outside this calculation.
How baluster spacing is calculated
For a clear bay L, finished baluster width W and N balusters, the unrounded equal clear gap is (L − N × W) ÷ (N + 1). A centre mark is one gap plus half a baluster width from the left inside post, then one gap and one full width for each next baluster. The calculator rounds each absolute centre position to your tape increment and checks both end gaps and every interior gap. If one exceeds your chosen maximum, it tries another baluster.
Why the rounded plan can need one more
For a 27 1/8 in opening and 5/8 in balusters, five balusters give ideal 4 in gaps. With marks rounded to the nearest 1/8 in, the first centre moves to 4 3/8 in and its clear end gap becomes 4 1/16 in. The calculator uses six balusters to keep the actual planned gaps within a 4 in maximum.
What to measure and check
Measure the opening at the line where the balusters will be fitted, from the left inside post face to the right inside post face. Measure the actual face width of the baluster. Enter the largest clear opening you want between surfaces; this is a project choice, not a built-in code judgment. Mark from the same fixed left origin rather than stepping repeatedly from a prior rounded mark. Confirm site dimensions, rail alignment, local rules and the product’s installation instructions before fixing.
Related planning tools
For a stair rise and run, use the stair stringer calculator. For decking quantities, use the deck board calculator. If you are spacing fence boards rather than railing balusters, use the fence picket calculator.
