# How to Calculate Stairs: Rise, Run & Number of Steps A step-by-step method for sizing a stair from your floor-to-floor height and available run — risers, riser height, going and total run — each checked against NCC 2025 limits and the 2R+G rule. - Canonical HTML: https://www.chippy.tools/building-codes/au/stairs/how-to-calculate-stairs/ - Publisher: Chippy Tools - Updated: 2026-09-06 - Market: au - Code edition / reference: NCC 2025 - References: HP 11.2 - Scope: Australia; Class 1 and 10 Housing Provisions. Confirm local adoption and variations. - Source text checked: 2026-09-06 - Review scope: Official source cross-check; not a site-specific compliance assessment. ## The method, in one line Divide your total rise in millimetres by **190** and round up. This gives the fewest risers that meet the maximum height. Divide the rise by that count to get the riser height, then check the other limits. For one straight flight with the upper floor as the final tread, there is one fewer going than risers. Pick a going between **240 mm and 355 mm** that fits your run. Then check that 2R+G lands between **550 mm and 700 mm**. Your two starting numbers are already on site. The total rise is the floor-to-floor height. The available run is how much floor length you have to fit the stair into. Every other number comes from those two. Here’s what each term means: - Rise: the total height, floor to floor. - Run: the total floor length the stair takes up. - Riser (R): the height of one step. - Going (G): the depth of one step, nose to nose. - 2R+G: a comfort check. Two step heights plus one step depth must land in a set range. And here are the limits the rule book sets (NCC 2025, clause 11.2): | Dimension | Limit (NCC 2025) | |-------------------|-----------------------------------| | Riser (R) | max **190 mm** · min **115 mm** | | Going (G) | max **355 mm** · min **240 mm** | | 2R + G | between **550 mm** and **700 mm** | | Risers per flight | max **18** before a landing | **Diagram labels:** 2700 mm = 15 × 180 mm; 3500 mm = 14 × 250 mm; R = 180 mm (≤ 190 mm); G = 250 mm (240–355 mm) NCC 2025 Housing Provisions 11.2 Two things to get straight before you start. This example has one straight flight with the upper floor as the final tread. It has one fewer going than risers. Other top details, turns and separate flights need their own set-out. And every step has to be the same height, every going the same depth. The odd step out is where people trip. ## How to calculate stairs by hand Say your floor-to-floor height is **2700 mm**. You have **3600 mm** of floor length to fit the stair into. Here’s how it goes, step by step. 1. **Work out the number of steps.** Divide the total rise by the top step height, then round up: 2700 ÷ 190 = 14.2. You can’t have part of a step, so round up to **15 risers**. 2. **Work out the step height.** Divide the rise back by that number so every step is even: 2700 ÷ 15 = **180 mm** per step. Check it: 180 is under the 190 mm top limit and over the 115 mm bottom limit. Good. 3. **Work out the number of goings.** One fewer than the number of steps: 15 − 1 = **14 goings**. 4. **Pick a going that fits your run.** The deepest going you can fit is your floor length divided by the number of goings: 3600 ÷ 14 = 257 mm. So anything up to about 257 mm fits. Pick a round **250 mm**. Check it: 250 is inside the 240 mm and 355 mm limits. Good. 5. **Work out the total run.** Number of goings times the going: 14 × 250 = **3500 mm**. That fits inside the 3600 mm you had. Good, with 100 mm to spare. 6. **Run the 2R+G comfort check.** (2 × 180) + 250 = **610 mm**. That’s inside the 550–700 range. This checks that formula. So: **15 steps at 180 mm, 14 goings at 250 mm, 3500 mm of run.** These example dimensions meet the limits in the table above. They do not check the whole stair design, including headroom, landings, handrails and barriers. If step 6 falls outside 550–700 mm, revise the layout and check all the limits again. Adding a riser lowers each riser but also adds a going; it does not automatically make the stair fit a short run. If a flight needs more than **18 risers**, plan a landing and check each flight on its own. ## Calculate and keep your working [Download the Chippy Tools stair set-out worksheet](https://www.chippy.tools/building-codes/printables/) to record your inputs and the approved requirements. ## Keep reading - [NCC stair requirements: riser, going & the 2R+G rule](https://www.chippy.tools/building-codes/au/stairs/ncc-stair-requirements/) has every limit this method checks against, in full. - [Maximum & minimum stair riser heights in Australia](https://www.chippy.tools/building-codes/au/stairs/stair-riser-heights/) covers the step-height numbers on their own. It also covers what happens when a stair is a few millimetres out. - Part of the [stairs cluster](https://www.chippy.tools/building-codes/au/ncc-for-chippies/). Start here for the whole NCC stairs picture. ## Sources - **NCC 2025, ABCB Housing Provisions Standard, clause 11.2** — stairway construction (riser, going, 2R+G, risers per flight). Confirm every figure at [the official NCC provision](https://ncc.abcb.gov.au/editions/ncc-2025/adopted/housing-provisions/11-safe-movement-and-access/part-112-stairway-and-ramp-construction). *(Clause number and values are confirmed against the NCC 2025 Housing Provisions Standard, source text checked 2026-09-06.)* Still on NCC 2022? This article is written against NCC 2025. NSW and SA don't adopt NCC 2025 until 1 May 2027, and Tasmania has frozen its residential changes — so if your job is being certified under NCC 2022, confirm the requirement against that edition. Core stair and room geometry is largely unchanged between editions; where a number did change, it's called out in the article body. Content adapted from the National Construction Code 2022, provided by the Australian Building Codes Board under the CC BY 4.0 licence. This page is general information for tradespeople and is not compliance, engineering or legal advice. Requirements are subject to state and territory variations and adoption timing. Always confirm requirements with your building certifier and relevant state authority. ## Frequently asked questions ### How do I work out how many steps I need? Divide the total rise in millimetres by 190 and round up. That gives the fewest risers that meet the maximum height in this scope. Divide the rise by that count, then check the resulting height, going, flight count and 2R+G against the rules and available space. ### How do I calculate riser height and going? Step height is the total climb divided by the number of steps. The going is how deep each tread is. Pick a depth inside the limits, check it fits the floor space you have, then check that two step heights plus one tread depth lands in the 2R+G range. ### What's the difference between rise, run and going? Rise is the total height, floor to floor. Run is the total floor length the stair takes up. Going is the depth of one step, nose to nose. Total run is the number of tread depths times the going. ### How many risers can you have before you need a landing? One run of stairs can have no more than 18 steps before you need a landing. If your step count comes out higher than that, break the stair with a landing so no single run goes over the limit. ### Does the going include the nosing overhang? No. The going is measured from the front edge of one tread to the front edge of the next. That's the depth you actually walk on. The tread board can stick out over the step below it (the nosing), but that overhang does not add to the going. ## Source-check references - [NCC 2025 Housing Provisions 11.2.2 and Table 11.2.2a; 11.2.5](https://ncc.abcb.gov.au/editions/ncc-2025/adopted/housing-provisions/11-safe-movement-and-access/part-112-stairway-and-ramp-construction)