Equal spacing means every clear gap is the same: the gap beside the first post, every gap between balusters, and the gap beside the last post. Calculate the whole baluster count first, then divide the leftover clear space by one more than that count.
The baluster-spacing calculator returns the equal clear gap and centre-to-centre spacing. Use the clear gap for a spacer block; use centre spacing only when your layout method and product instructions call for centre marks.
Check the layout
- Measure the finished clear width between post faces.
- Measure the actual baluster face width.
- Verify the maximum clear opening permitted for the project.
- Calculate the minimum whole baluster count.
- Mark the first baluster at one equal gap from the post.
- Continue with a spacer cut to the calculated clear gap, or mark repeated centre spacing from one fixed reference.
- Dry-fit the complete opening and measure the final gap before fastening.
Worked example: a 72-inch opening
For a 72-inch clear opening, 1.5-inch balusters, and a user-selected 4-inch maximum gap:
- Minimum count:
ceil((72 - 4) / (1.5 + 4)) = 13. - Width occupied by balusters:
13 x 1.5 = 19.5 inches. - Space left for gaps:
72 - 19.5 = 52.5 inches. - Number of gaps:
13 + 1 = 14. - Equal clear gap:
52.5 / 14 = 3.75 inches. - Centre-to-centre spacing:
3.75 + 1.5 = 5.25 inches.
The first baluster begins 3.75 inches from the post face. A 3.75-inch spacer then repeats every clear gap. Do not add a separate end correction: the equation already includes both end gaps.
Choose a transfer method
- Spacer block: useful when baluster faces are parallel and the product can be dry-fitted. Cut one test spacer to the calculated clear gap.
- Centre marks: useful with a template or predrilled rail. Start from a single reference face and repeat the calculated centre spacing; do not move the tape origin after every mark.
- Story stick: useful across several identical openings. Mark the complete tested layout on scrap, identify its opening width, and do not reuse it for a different width.
Mistakes that produce an uneven final gap
- Measuring and marking from alternate ends.
- Rounding the equal gap too early.
- Using nominal rather than actual baluster width.
- Allowing a spacer block to collect sawdust or sit at an angle.
- Multiplying a rounded centre spacing across a long opening instead of checking the last position.
- Forcing a layout by narrowing, notching, or modifying a baluster contrary to its instructions.
If the final dry-fit does not match, remeasure the clear opening and actual baluster width rather than hiding the remainder in one gap. The separate baluster quantity guide explains how whole counts are selected.
The measurement guide shows how to enter feet, inches, fractions, and metric values without converting them by hand.
Limits and sources
The common 4-inch planning preset is not universal. Verify the adopted code, stair exceptions, product evaluation documents, and manufacturer instructions for the actual project. The 2021 IRC, Section R312.1.3 is one US residential-code reference. The American Wood Council DCA 6 guide provides deck and guard context while expressly deferring to the authority having jurisdiction. See the railing formula methodology for the exact MaterialNest equation.
Reviewed: July 29, 2026. Sources were checked on that date. Report a possible correction to feedback@materialnest.com.