Evenly spaced spindles look professional and keep a guard within code. Rather than spacing by eye, measure the clear distance between the posts and let the arithmetic decide the gap. Cut a spacer block to the calculated gap and work from one post to the other.
How to use the Spindle Spacing Calculator
- Distance between posts
- Spindle width
- Maximum gap
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the clear distance between the posts, the spindle width and the largest gap allowed. The calculator rounds the number of spindles up so the gap is never exceeded, then divides the remaining space equally.
Tip
Cut a spacer block to the exact gap and use it at the top and bottom of each spindle; small errors then cannot accumulate along the rail.
Tips for an accurate estimate
- Sketch the job and split irregular areas into rectangles, circles and triangles before you measure.
- Add a waste allowance – typically 5–10% for simple layouts and 15–20% for diagonal, curved or heavily cut work.
- Check the coverage or yield printed on the product, because sizes and densities vary between manufacturers.
- Buy all units of a finished material (tile, brick, siding) from the same batch so colours match, and keep a few spares for repairs.
- Confirm local prices – quarry, lumber and steel prices vary widely by region and season.
Common mistakes to avoid
- Ordering exactly the calculated amount with no allowance for breakage, offcuts and settlement.
- Forgetting to subtract doors, windows and other openings – or subtracting small ones that still need cutting around.
- Confusing US short tons (2,000 lb) with metric tonnes (1,000 kg) when comparing quotes.
Inputs explained
| Field | What to enter |
|---|---|
| Distance between posts | Units: in, cm, mm, ft, m |
| Spindle width | Units: in, cm, mm, ft, m |
| Maximum gap | Units: in, cm, mm, ft, m |
What each result means
- Number of spindles = ceil(([Distance between posts] – [Maximum gap])÷([Spindle width] + [Maximum gap]))
- Exact gap = ([Distance between posts] – [Number of spindles]×[Spindle width])÷([Number of spindles] + 1)
- Exact gap (decimal) = ([Distance between posts] – [Number of spindles]×[Spindle width])÷([Number of spindles] + 1)
- On-centre spacing = [Exact gap (decimal)] + [Spindle width]
- First spindle centre from post = [Exact gap (decimal)] + [Spindle width]÷2
Example values
How the main result changes when Distance between posts changes and everything else stays at the example values above:
| Distance between posts (in) | Number of spindles |
|---|---|
| 36 | 6 |
| 54 | 10 |
| 72 | 13 |
| 90 | 16 |
| 108 | 19 |
| 144 | 26 |
Formula
n = ceil((L − g) ÷ (w + g))Gap = (L − n × w) ÷ (n + 1)On-centre = gap + w; first centre from post = gap + w ÷ 2Worked example
Inputs — Distance between posts: 72 in; Spindle width: 1.5 in; Maximum gap: 4 in.
Results — Number of spindles = 13; Exact gap = 3 3/4; Exact gap (decimal) = 3.75 in; On-centre spacing = 5.25 in; First spindle centre from post = 4.5 in.
Frequently asked questions
How do I space balusters evenly?
Measure between posts, choose the number of spindles that keeps the gap under 4 in, then divide the leftover space by the number of gaps (spindles + 1).
Should I start at a post or centre the layout?
Starting with a full gap at each post, as here, gives a symmetrical layout.
What if my spindles are square-turned?
Use the widest part of the spindle as its width.
What formula does the Spindle Spacing Calculator use?
n = ceil((L − g) ÷ (w + g)).