Baluster Spacing Calculator (Metric)
Find how many balusters you need and the even gap between them for a railing, keeping every gap within the standard 4-inch code limit.
What your result means
Balusters needed is how many spindles fit while keeping every gap at or below your maximum, spaced evenly. Even gap is the resulting space between each baluster and at the ends. Most building codes require that a 4-inch sphere cannot pass through any gap, so keep it under 10.2 cm. Measure your run first with our measuring tools if needed.
How to use this calculator
- Measure the clear railing length between posts, in inches.
- Enter your baluster width (3.8 cm for 2x2, 1.9 cm for square).
- Set the maximum gap — keep it under 10.2 cm for code.
- Read the number of balusters and the even gap.
- Lay out from the center so the end gaps match.
The formula
The count is the fewest balusters that keeps every gap at or under your maximum. Dividing the leftover space by the number of gaps (one more than the balusters) gives the even spacing.
Worked example
A 96-inch railing with 1.5-inch balusters and a 4-inch max gap needs ceil((96 - 4) / (1.5 + 4)) = 17 balusters. The even gap works out to (96 - 25.5) / 18 = 10 cm — just under the 4-inch limit.
Baluster spacing rules
| Item | Typical value |
|---|---|
| Max gap (most codes) | < 10.2 cm (4-in sphere rule) |
| 2x2 baluster width | 3.8 cm |
| Square baluster width | 1.9 cm |
| Stair guard gap | < 4 3/20.3 cm (varies) |
| Guard height | 36 - 106.7 cm (varies) |
Tips & gotchas
- The 4-inch rule: a 4-inch sphere must not pass through any gap — keep gaps a hair under.
- Lay out from the center of the railing so the two end gaps are equal.
- Stairs sometimes allow a slightly larger gap (4 3/20.3 cm) — check your local code.
- Account for the baluster's actual width, not its nominal name.
- Confirm guard height and gap rules with your local building department.
Frequently asked questions
What is the maximum gap between balusters?
Most codes require gaps small enough that a 4-inch sphere can't pass, so under 10.2 cm. Some stair guards allow up to 4 3/20.3 cm — check local code.
How do I space balusters evenly?
Find the count that keeps every gap under the limit, then divide the leftover space by the number of gaps (balusters plus one) and lay out from the center.
How many balusters do I need?
It depends on railing length, baluster width, and max gap. A 96-inch railing with 1.5-inch balusters at a 4-inch max gap needs about 17.
What's a common baluster width?
3.8 cm for a 2x2 wood baluster and about 1.9 cm for square metal balusters. Use the actual measured width.
Does the code differ for stairs?
Sometimes. Stair guards may permit a slightly larger gap than level railings. Always verify with your local building department.
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