Baluster spacing chart
Balusters and the gap they leave, by clear span, for 2x2 stock. Every row keeps the opening under the 4" sphere a guard has to refuse.
| Clear span | Balusters | Gap | Under the sphere by |
|---|---|---|---|
| 36" | 7 | 3 3/16" | 13/16" |
| 48" | 9 | 3 7/16" | 9/16" |
| 60" | 11 | 3 5/8" | 3/8" |
| 72" | 14 | 3 3/8" | 5/8" |
| 84" | 16 | 3 1/2" | 1/2" |
| 96" | 19 | 3 3/8" | 5/8" |
| 120" | 23 | 3 9/16" | 7/16" |
Reading it
- IRC R312.1.3 says no opening in a guard may pass a 4" sphere. It is a sphere, not a flat gap, so an opening measured at exactly four inches fails.
- 2021 IRC, and defaults rather than law. Jurisdictions amend it and the building department decides.
- Measure the clear span between posts, not the rail's overall length. Sections are rarely all the same, and a count that is right for one is over the limit on the next.
For the case this table does not cover
- Baluster and slat spacing
Even gaps across any span, checked against the 4-inch guard rule, with tape-measure marks that don't drift.
- Deck and fence takeoff
Boards, joists, posts, pickets, screws and bags of concrete, with the gaps between boards properly counted.
- Stair stringers
Divide the rise into even risers, lay out the notches, and check the result against the code.