Get the australian standard stair dimensions wrong and you’ve got a building surveyor sign-off problem, an insurance problem, and a slip-and-fall liability problem all rolled into one. Stairs are one of the most heavily regulated elements in any Australian build because they’re statistically one of the most dangerous. The good news: the rules are clear, the maths is simple, and once you understand the framework, getting compliant stairs right every time becomes second nature.

This guide breaks down exactly which standard applies to your project, the rise and run limits enforced by the National Construction Code (NCC), the 2R+G formula every chippy should know by heart, and the most common compliance traps that get pulled up at inspection. Whether you’re a licensed builder, carpenter, certifier or owner-builder, this is the reference you’ll come back to.

Which Standard Applies to Your Stairs?

Australia uses different stair standards depending on the building class and use:

• NCC Volume One, Part D3 — applies to Class 2 to 9 buildings (commercial, multi-residential, public buildings).
• NCC Volume Two, Part H1D7 — applies to Class 1 (houses) and Class 10a (sheds, garages, carports) buildings.
• AS 1657:2018 — applies to fixed platforms, walkways, stairways and ladders for industrial use, plant access and rooftop access.
• AS 1428.1:2021 — applies where accessibility for people with a disability is required (Class 3, 5, 6, 9 buildings and accessible paths in Class 2).

The NCC 2022 edition is currently in force across most states and underpins the dimensions discussed below. Always check the version adopted in your state and any state variations (NSW, QLD and VIC each have minor amendments).

Residential vs Commercial vs Industrial Stair Requirements

Residential (Class 1 and 1a private stairs) have the most flexible dimensions because they’re used by familiar occupants. Riser heights up to 190mm and goings down to 240mm are permitted.

Commercial and public stairs (Class 2-9) have tighter limits because they serve a broader range of users including elderly occupants, children and visitors unfamiliar with the layout. The maximum rise drops, the minimum going increases, and additional accessibility requirements kick in for any stair on an accessible path of travel.

Industrial stairs covered by AS 1657 are designed for trained workers accessing plant. They permit steeper pitches (up to 45 degrees) and narrower goings, but mandate stricter slip resistance, kick plates and handrails on both sides.

Rise and Going (Run) Requirements Under the NCC

The riser is the vertical face of the step; the going (also called the run or tread depth) is the horizontal distance between the nosings of two consecutive treads. NCC limits for stairs in private dwellings (Class 1) are:

• Riser (R): minimum 115mm, maximum 190mm
• Going (G): minimum 240mm, maximum 355mm
• Tread quantity: minimum 2 risers per flight

For Class 2 to 9 buildings (commercial and multi-residential), the limits tighten:

• Riser: minimum 115mm, maximum 190mm (same)
• Going: minimum 250mm, maximum 355mm
• Quantity: minimum 2 risers per flight

Within a single flight, every riser must be the same height and every going must be the same depth (with allowable construction tolerance discussed below). Mixed risers are one of the fastest ways to fail an inspection and a leading cause of trip injuries.

The 2R+G Formula: The Stair Designer’s Rule of Thumb

The NCC mandates that the slope relationship of stairs satisfies:

2R + G must be between 550mm and 700mm

This is the single most important stair formula in Australian construction. It ensures the stair pitch matches the natural human gait — too steep and the stair feels dangerous, too shallow and the stride feels awkward. A few worked examples:

• Rise 170mm, going 250mm: 2(170) + 250 = 590mm (compliant, comfortable domestic stair)
• Rise 190mm, going 240mm: 2(190) + 240 = 620mm (compliant, steep but legal in Class 1)
• Rise 150mm, going 300mm: 2(150) + 300 = 600mm (compliant, generous public stair)
• Rise 200mm, going 230mm: 2(200) + 230 = 630mm (FAIL — rise exceeds 190mm and going under 240mm)

For a fast, no-error setout, run your dimensions through the free Built Simple stair calculator — it cross-checks rise, going and 2R+G all in one go and flags non-compliance before you cut a single stringer.

Maximum Flights and Landings

The NCC limits a single stair flight to 18 risers maximum before a landing is required. The minimum is 2 risers per flight (single-step trip hazards are explicitly disallowed in many circumstances).

Landing requirements:

• Length: at least 750mm in the direction of travel for domestic, 1000mm for Class 2-9 buildings.
• Width: not less than the width of the stair flight it serves.
• Slope: landings must not slope more than 1:50 (effectively level).
• Doorway clearance: a door swinging onto a landing must not encroach more than half the landing depth.

Tread Types and Slip Resistance

Treads can be closed (with a riser board) or open (no riser board, common in modern designs). If treads are open, the gap must not allow a 125mm sphere to pass through — the same balustrade rule discussed below.

Nosings must be visually contrasting (a 50-75mm strip of contrasting colour or a slip-resistant nosing) on stairs serving the public or accessible paths under AS 1428.1.

Slip resistance is classified by AS 4586 pendulum or ramp tests:

• R10: minimum for internal dry stairs in commercial buildings.
• R11: required for external stairs and any wet-area stairs (pool surrounds, bathrooms, entry porches exposed to weather).
• R12 / R13: commercial kitchens, industrial wet areas.

Handrail Requirements

Handrails are mandatory on at least one side of any stair with 4 or more risers (NCC). Both sides are required where the stair serves an accessible path under AS 1428.1, or where the stair is more than 2m wide.

• Height: 865mm minimum, 1000mm maximum measured vertically from the nosing line for general use. Where the same rail acts as a balustrade on a stair more than 1m above adjacent surface, the upper limit extends to 1200mm and the rail/balustrade must comply with both functions.
• Continuity: handrails must be continuous along the full flight and turn through landings on accessible stairs (AS 1428.1).
• Graspability: circular profile 30-50mm diameter, or equivalent gripping cross-section. A clear 50mm gap between the rail and any wall.
• Extensions: AS 1428.1 requires handrails to extend 300mm horizontally beyond the top and bottom risers on accessible stairs.

Balustrade Gap Rules: The 125mm Sphere

Where a stair, landing or balcony is more than 1m above the surface beneath, a balustrade is mandatory. Key dimensions:

• Minimum height: 865mm above the stair nosing line, or 1m above a landing or floor.
• Opening size: any opening must not allow a 125mm sphere to pass through (this is the classic NCC 125mm rule).
• No climbable elements: between 150mm and 760mm above floor level on balconies more than 4m above ground, balustrades must not contain horizontal or near-horizontal elements that a child could climb.

For sloped or raked walls and gable ends adjacent to stairs, our raked wall two heights calculator gives you the framing dimensions in seconds.

Headroom Clearance

The NCC mandates a minimum vertical headroom of 2000mm measured from the nosing line of any tread. This is non-negotiable and one of the most common failures in retrofit stairs squeezed into existing voids. Always verify headroom early in your stair setout — adjusting later usually means moving a wall or a floor opening.

Construction Tolerances

Even with perfect drawings, on-site construction varies. The NCC allows a maximum variation of:

• 5mm between consecutive risers in a single flight.
• 10mm between the largest and smallest riser across the whole flight.
• 5mm between consecutive goings.
• 10mm between the largest and smallest going across the flight.

Setting out from a single datum line, using a stair gauge on your framing square, and pre-cutting all stringers from the same template is the easiest way to stay inside tolerance.

Common Stair Compliance Failures

The top issues building surveyors flag:

• Inconsistent risers — usually the bottom or top step where the floor finish wasn’t accounted for.
• Going too short — common on tight retrofits where designers compress the stair to fit available run.
• 2R+G outside 550-700mm — typically too steep, exceeding 700mm.
• Handrail too short or too tall — often installed using off-the-shelf brackets without checking the stair pitch.
• Balustrade gaps over 125mm — particularly on horizontal wire balustrades that flex over time.
• Insufficient headroom under bulkheads or upper landings.
• Open risers not satisfying the 125mm rule on stairs above 1m drop.
• Missing slip resistance certification on external or wet-area stairs.

Free Built Simple Stair Calculator

Doing the maths by hand for every stair is slow and error-prone. The free Built Simple stair calculator lets you input total rise, available going and stair width, then instantly returns:

• Number of risers and goings
• Exact rise and going dimensions to the millimetre
• 2R+G compliance check
• Total stair length and angle
• Stringer length and cut dimensions

It also flags any breach of NCC limits before you commit to a setout. Pair it with the rest of the Built Simple calculator suite for framing, roofing, decking and concrete takeoffs — all built specifically for Australian standards.

FAQs

What is the standard step height in Australia?

Riser height must be between 115mm and 190mm under the NCC. The most comfortable domestic riser sits around 170-180mm; commercial stairs typically use 150-170mm risers for easier access.

What is the standard rise and run of stairs?

A typical compliant Australian domestic stair uses a 175mm riser with a 250-280mm going. This satisfies the 2R+G formula with a result around 600-630mm and produces a comfortable, code-compliant pitch of around 32-35 degrees.

What is the stair formula 2R+G?

Twice the riser height plus the going must equal between 550mm and 700mm. It’s a human-factors formula that ensures the stair matches natural walking gait — outside this range stairs feel dangerously steep or awkwardly shallow.

Can I have open risers on a domestic stair?

Yes, but only if the gap between treads does not allow a 125mm sphere to pass. On stairs more than 1m above the surface below, this rule applies strictly.

How many risers can I have before needing a landing?

Eighteen risers maximum per flight under the NCC. Beyond that, a compliant landing is required before continuing the stair.

Do I need a handrail on a 3-step stair?

The NCC requires handrails on stairs with 4 or more risers. Three risers technically don’t require one, but most designers and certifiers recommend installing a rail anyway for occupant safety, particularly for elderly users or accessible paths.

Get your dimensions right the first time, document the 2R+G calculation in your shop drawings, and your stair will pass surveyor inspection without drama. When in doubt, run the numbers through the Built Simple stair calculator before you cut.