The three numbers a stair has to hit
Australian private stairs are dimensioned against three published limits, and a design has to sit inside all three at once.
| Dimension | Published range for a private stair | What it controls |
|---|---|---|
| Riser (R) | 115 to 190mm | How far your foot lifts each step |
| Going (G) | 240 to 355mm | How much tread your foot lands on |
| 2R + G | 550 to 700mm | Whether the two suit each other |
Riser and going on their own aren't enough. A 190mm riser with a 240mm going gives 2R+G = 620, which is fine. A 120mm riser with a 355mm going gives 595, also fine. But a 190mm riser with a 355mm going gives 735, which is out, and that's the whole point of the third check.
The ranges are clause 11.2.2 of the ABCB Housing Provisions, and the numbers are the same in the 2025 edition and the 2022 edition, both free to read and both read 26 October 2026. Which one you build to depends on your state. NCC 2025 started in Victoria, WA and the ACT on 1 May 2026, and NSW, Queensland, SA and Tasmania stay on NCC 2022 until 1 May 2027. The same clause caps a flight at 18 risers and floors it at 2, because a single step is a trip hazard, not a stair.
2R + G on stairs
2R + G is two riser heights plus one going. On a private stair in Australia it has to land between 550 and 700mm, and around 620 to 640mm is the stair nobody notices. A 180mm riser and a 265mm going is (2 × 180) + 265 = 625mm, right in the middle.
It's a stride rule, about 350 years old. A person walking on the flat takes a step of roughly 620 to 640mm, and climbing, each unit of rise costs about twice the effort of the same unit of travel, so a comfortable stair keeps two risers plus one going close to that flat stride. The French architect Blondel wrote it down as 2R + G ≈ 630mm in the 1670s and it has survived every building code since, because feet haven't changed.
A worked example, 2700mm floor to floor
Standard 2.7m floor-to-floor in a two-storey house, aiming for a riser around 175mm.
- 2700 ÷ 175 = 15.4, so go with 15 risers
- Riser height, 2700 ÷ 15 = 180.0mm exactly, inside 115 to 190
- Goings, 15 − 1 = 14 treads
- Pick a 265mm going, and 2R+G = (2 × 180) + 265 = 625mm, nicely mid-range
- Floor space used, 14 × 265 = 3710mm. That's 3.7 metres of floor gone, and you still need landing room at both ends.
- Stringer, √(2700² + 3710²) = 4588mm, so order 4.8m stock
- Pitch, 180 over 265, 34.2°, the angle you set the stringer at
Try 14 risers instead and the riser height becomes 2700 ÷ 14 = 192.9mm, which is outside the 190mm limit. Go the other way to 16 risers and the riser drops to 168.8mm, comfortable, but the stair now needs about 4.3m of floor instead of 3.7m. Six hundred millimetres of hallway is often what actually decides the riser count.
Every riser has to be the same
This is the one that fails inspections and hurts people. Risers within a flight must be equal, and the published tolerance is concrete. Adjacent risers may differ by no more than 5mm, and the biggest and smallest riser in the whole flight by no more than 10mm (ABCB Housing Provisions 11.2.2, read 26 October 2026). Your foot learns the rhythm in two steps and stops looking after that, so a bottom step 15mm shorter than the rest is a trip waiting to happen, and it will be found by the person carrying a laundry basket.
Where it goes wrong, almost every time, the floor finishes weren't in the measurement. You set the stair off a bare slab, then 20mm of tile and bed goes down at the bottom and 19mm of engineered timber goes down at the top. Now the bottom riser is 20mm short, the top riser is 19mm tall, and every riser in between is right. Measure finished floor level to finished floor level. If the finishes aren't decided yet, decide them before you cut a stringer.
Floor-to-floor heights and what they give you
| Floor to floor | Risers | Riser height | Treads | Floor space used |
|---|---|---|---|---|
| 2400 mm | 14 | 171.4 mm | 13 | ~3.67 m |
| 2550 mm | 15 | 170.0 mm | 14 | ~3.99 m |
| 2700 mm | 15 | 180.0 mm | 14 | ~3.71 m |
| 2850 mm | 16 | 178.1 mm | 15 | ~4.03 m |
| 3000 mm | 17 | 176.5 mm | 16 | ~4.35 m |
Each row uses the going this calculator suggests, which centres 2R+G in its range. Change the going and the floor space changes with it, and that's usually the lever you pull when the stair doesn't fit.
The things a rise-and-going sum doesn't cover
- Flight length. Published guidance caps a flight at 18 risers before you need a landing, and a flight needs at least two risers, because a single step is a trip hazard, not a stair.
- Headroom. Two metres measured vertically off the nosing line is the figure to design to. Check it against the floor structure above before you set the opening out.
- Nosings. A projecting nosing adds tread without adding going. There's a limit on how far it can stick out, and open risers have to pass the same 125mm sphere test as a barrier.
- Barriers and handrails. Where the drop is more than a metre you need a barrier, 865mm measured above the nosing line on the flight, 1000mm on a landing. Our balustrade spacing calculator does the baluster maths.
- Winders. Legal, but their going is measured differently and they're the fiddliest part of any stair. Fit a straight flight with a landing if you possibly can.
Cutting the stringer
The stringer length above is the raw diagonal along the nosing line. A cut string loses depth at every notch, so start from stock deep enough to keep sound timber behind the cuts. 290 or 300mm deep is normal. A housed string keeps its full section because the treads sit in routed trenches instead, which is why it's the stronger detail on a long flight. Add cutting allowance at both ends and buy the next length up.
Stair set out. Now get it priced and invoiced.
Yamate turns your materials and hours into a quote the customer can accept on their phone, then an invoice, then a payment, with the GST handled and payment reminders sent once you switch them on.
Try Yamate free → Free to try · no card · sign in with a link, no password to rememberStairs FAQ
What are the Australian standard stair dimensions?
For a private stair, risers 115 to 190mm, goings 240 to 355mm, and 2R + G between 550 and 700mm. A flight has 2 to 18 risers, and its risers stay within 5mm of the next one and 10mm across the whole flight. Those come from the ABCB Housing Provisions, clause 11.2.2. Your certifier or building surveyor signs the stair off, not the calculator.
What is the maximum riser height in Australia?
190mm for a private stair, with a minimum of 115mm, as published for NCC Volume Two. A 2700mm floor-to-floor divided by 14 risers gives 192.9mm, which is over, so you need 15.
What is the minimum going for stairs in Australia?
240mm, with a maximum of 355mm, for a private stair. The going is the horizontal tread depth from nosing to nosing, not the full board width including the overhang.
What is the 2R+G rule?
Two riser heights plus one going, which has to land between 550 and 700mm. It checks that the riser and the going suit each other, because either one can be inside its own range while the pair is uncomfortable to walk. Around 620 to 640 is the sweet spot.
How many stairs for a 2700mm floor to floor?
15 risers at 180mm each, giving 14 treads. 14 risers would be 192.9mm which is over the 190mm limit, and 16 gives a gentler 168.8mm but eats about 600mm more floor.
Why is the number of treads one less than the risers?
Because the top riser lifts you onto the upper floor, and the upper floor is the tread. A flight with 15 risers has 14 treads. Cut 15 treads and you have a spare.
Do all the risers have to be the same height?
Yes. Within a flight, adjacent risers may differ by no more than 5mm and the largest and smallest by no more than 10mm, per the ABCB Housing Provisions. The usual cause of an odd one is measuring off a bare slab and then adding tiles or timber. Measure finished floor to finished floor.
How do I work out the stringer length?
Pythagoras. Square the total rise, square the total going, add them, take the square root. For 2700mm rise and 3710mm of going that's 4588mm, then add cutting allowance and buy the next stock length up.
Other calculators you'll want
General information for Australian trades, and an estimate only, not tax, financial or legal advice. It is not engineering, building or design advice either. A calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. Riser, going and 2R+G ranges here follow published Australian guidance on the NCC Volume Two private-stair rules. The NCC and the Australian Standards it references are published and sold by their publishers and are not reproduced here, and editions change. This tool reports whether a dimension is inside or outside the published range. It does not sign a stair off. Confirm any stair you're going to build with your certifier or building surveyor.