Guardrail & Baluster Calculator

Railing span (between posts)

The clear opening between the two guard posts.

Baluster width

Width of one picket — 1½″ for a 2×2, ¾″ for many metal balusters.

Maximum gap

Code reference

Balusters needed11

Even gap3-5/8" · 92.1 mm

On-center spacing5-1/8" · 130.2 mm

11 balusters give an even 3.63″ gap — under the 4.00″ maximum (a sphere that size must not pass).
Gaps are equal at each end (post-to-baluster) and between balusters.

Guard requirements — Residential (IRC)

2021 IRC §R312.1

Where requiredOpen sides more than 30″ above grade (762 mm)§R312.1.1

Guard height36″ min (914 mm)§R312.1.2

Guard at open side of stairs34″ min from nosing line (864 mm)§R312.1.2

When guard top is the handrail (stairs)34″ – 38″ (864 – 965 mm)§R312.1.2

Infill openingsNo 4″ sphere passes (102 mm)§R312.1.3

Triangle at stair (riser/tread/rail)No 6″ sphere passes (152 mm)§R312.1.3

Openings on open side of stairsNo 4⅜″ sphere passes (111 mm)§R312.1.3

Where required: Measured to the floor or grade below at any point within 36″ horizontally.