Balustrade Spacing Calculator
Calculate baluster count and spacing to meet the NCC 125mm maximum opening rule.
Estimate only — not a substitute for a licensed tradesperson, a certified engineer, or sign-off from your local building surveyor. Verify against current standards and site conditions before ordering materials or starting work.
Result
- Balusters required
- 20
- Actual gap achieved
- 115.79mm
If the balusters are too wide to fit the run, the achieved gap shows 0 rather than a negative number - reduce the baluster width or lengthen the run. A gap of 0 is not a compliant balustrade, it means the layout does not work.
NCC Housing Provisions clause 11.3.4(4): openings in barriers, INCLUDING decorative balustrades, must not permit a 125mm sphere to pass through; for stairways the opening is measured above the nosing line of the treads. Verified 2026-08-31 by reading the expanded clause text directly on ncc.abcb.gov.au (NCC 2022). Note the exception: clause 11.3.4(7) allows a 300mm sphere ONLY for a barrier to a stairway serving a NON-HABITABLE room such as an attic or storeroom not used on a regular or daily basis - that exception does not apply to a normal balcony, deck or stair balustrade. Related: 11.3.4(2) sets barrier heights (not less than 865mm above stair nosings, not less than 1m above a landing, balcony, deck or the like), and 11.3.4(5) limits any gap between the barrier and the vertical face it is fixed to, to 40mm. Pool barriers are separate (H7D2 / AS 1926). NCC 2022 remains the legally operative edition in most states until each jurisdiction adopts NCC 2025 (NSW and QLD both 1 May 2027).
What this is based on
NCC Housing Provisions · 11.3.4(4)
Openings in barriers, including decorative balustrades, must not permit a 125 mm sphere to pass through. For stairways the opening is measured above the nosing line of the stair treads.
Checked against NCC 2022 on 2026-08-31
This calculator's 125 mm default IS the NCC limit for a normal balustrade - it is not a conservative design choice. Pool barriers are separate (H7D2 / AS 1926).
NCC Housing Provisions · 11.3.4(7)
Narrow exception: a barrier to a stairway serving a NON-HABITABLE room (attic, storeroom or the like, not used on a regular or daily basis) may instead use openings that do not permit a 300 mm sphere, or a top rail and intermediate rail arrangement.
Checked against NCC 2022 on 2026-08-31
Do NOT apply this to a balcony, deck or normal stair balustrade. It exists only for stairs to spaces like attics and storerooms.
NCC Housing Provisions · 11.3.4(2)
Barrier height: not less than 865 mm above stair tread nosings or a ramp floor, and not less than 1 m above the floor of a landing, corridor, balcony, deck, verandah or the like.
Checked against NCC 2022 on 2026-08-31
This calculator sizes baluster spacing only - it does not check barrier height.
NCC Housing Provisions · 11.3.4(5)
Where a barrier is fixed to the vertical face forming an edge of a landing, balcony, deck or stairway, the opening formed between the barrier and that face must not exceed 40 mm.
Checked against NCC 2022 on 2026-08-31
NCC Housing Provisions · 11.3.3
A continuous barrier is required along a trafficable surface where it is possible to fall 1 m or more from that surface to the surface beneath.
Checked against NCC 2022 on 2026-08-31
NSW is currently under NCC 2022. Adoption dates differ by state and territory — check yours before relying on any figure.
We cite the clause and link to the publisher so you can read the source yourself. We do not reproduce the text or tables of the NCC or of any Australian Standard.