Calculate rise, run, steps, stringer length and materials for straight, L-shaped, spiral and deck stairs — with AU, US and UK code checks.
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Written and reviewed by Mohsin Iqbal · Last reviewed August 2026
Every staircase starts from one number: total rise — the vertical floor-to-floor height it has to climb. Divide that by a comfortable riser height, round to a whole number of steps, then divide back so every riser ends up identical. Everything else — going, total run, stringer length, angle — follows from there.
Number of steps = round(Total rise ÷ Desired rise per step)
Actual rise = Total rise ÷ Number of steps
Total run = (Number of steps − 1) × Going
Stringer length = √(Total rise² + Total run²)
Stair angle = atan(Total rise ÷ Total run)
The number of treads is always one fewer than the number of risers — the top step leads onto the landing or upper floor, which isn't counted as a tread of its own.
| Term | Meaning |
|---|---|
| Rise | The vertical height of one step |
| Going (run) | The horizontal depth of one tread |
| Total rise | Full floor-to-floor vertical height |
| Total run | Full horizontal distance the staircase occupies |
| Riser | The vertical board at the back of each step (may be open or closed) |
| Tread | The horizontal board you step on |
| Stringer | The angled structural board the treads and risers are fixed to |
| Nosing | The front edge of a tread, often overhanging the riser slightly |
| Pitch / angle | The slope of the staircase, in degrees |
| Landing | A flat platform between flights |
| Headroom | Clear vertical space above the stair nosing line |
Rise and run trade off against each other: a taller riser means fewer steps for the same total rise, but a steeper, more tiring climb. A shorter riser needs more steps and more floor space, but feels gentler. The 2R + Going formula (twice the riser height, plus the going) is the standard way to check the balance — a result of roughly 550–700mm in Australia and the UK feels comfortable to walk; too low and the stair feels steep and cramped, too high and it feels like an awkward stretch between steps.
| Australia (NCC) | United States (IRC) | United Kingdom (Part K) | |
|---|---|---|---|
| Max riser | 190mm | 7¾″ (196.85mm) | 220mm |
| Min going | 240mm | 10″ (254mm) | 220mm |
| Comfort check | 2R+G: 550–700mm | 2R+G: 24–26″ (609.6–660.4mm) | 2R+G: 550–700mm |
| Min width | No NCC minimum for a private house stair; 1000mm applies only where AS 1428.1 accessibility is required | 36″ (914.4mm) | no fixed minimum in Part K itself |
| Max risers per flight | 18 (commonly cited) | 12 (commonly cited) | 16 (commonly cited) |
| Min headroom | 2000mm | 6'8″ (2032mm) | 2000mm |
These figures are commonly cited planning references, cross-checked against multiple independent trade and technical sources — not a substitute for the current, exact wording of your local code. Requirements are periodically updated and can vary by building class and jurisdiction, so always confirm your specific project against the current NCC, IRC or Approved Document K, or with your building surveyor.
| Angle | Feel |
|---|---|
| Under 30° | Very gentle, uses a lot of floor space |
| 30–38° | Comfortable residential range |
| 38–42° | Steeper, still common and generally code-compliant |
| Over 42° | Steep — exceeds the UK private-stair maximum pitch; check your local code carefully |
| Riser | Going | 2R+G | Feel |
|---|---|---|---|
| 175mm | 280mm | 630mm | Comfortable, common residential default |
| 180mm | 250mm | 610mm | Slightly steeper, space-efficient |
| 150mm | 320mm | 620mm | Gentle, uses more floor space |
| 190mm | 240mm | 620mm | At the maximum riser / minimum going for AU residential |
The rise/run geometry is identical indoors and out, but outdoor and deck stairs have extra practical considerations: treads need a slight drainage fall so water doesn't pool, materials need to handle weather exposure, and slip resistance matters more on a surface that gets wet. Check your local code for any outdoor-specific requirements before finalising a deck stair design.
Timber stairs are built from stringers (2 for narrow stairs, 3 or more for wider ones) with tread and riser boards fixed across them — material quantities scale with stringer length and board count. Concrete stairs are poured as a solid stepped mass, and the volume calculation is genuinely different: a staircase is a stack of rectangles, not a single uniform block, because concrete under an upper step still has to fill all the way down to the ground beneath it. A formula that just multiplies width × rise × going × number of steps treats every step as an identical isolated block and can understate the true volume by more than 80% on a typical flight — confirmed by direct calculation against the correct formula below.
Concrete stair volume = Width × Going × Rise × N(N+1) ÷ 2
where N is the number of steps
Deck stairs are usually a single short flight from ground level up to the deck surface, so total rise is often under 1–1.5m and the stair may only need 4–8 steps. The same code limits apply as any other stair — a common mistake is treating deck stairs as informal and skipping the riser-height check, which is exactly where an uneven or oversized step becomes a real trip hazard.
| Step | Working | Result |
|---|---|---|
| Number of steps | round(2400 ÷ 175) | 14 |
| Actual rise | 2400 ÷ 14 | 171.4mm ✓ |
| Total run | 13 × 260mm | 3.38m |
| Stringer length | √(2400² + 3380²) | 4.145m |
| 2R + Going | 2(171.4) + 260 | 603mm ✓ comfortable |
15 steps, actual rise 182.9mm (7.2in), total run 3.56m. 2R+going works out to 620mm — comfortably inside the 609.6–660.4mm (24–26in) range. At 15 risers, this flight would need a landing under the commonly-cited 12-riser IRC guidance — splitting it into two shorter flights.
15 steps, actual rise 173.3mm, total run 3.50m, 2R+going 597mm (comfortable), stringer length 4.360m — all within Part K's private-stair limits at a 36.6° pitch, under the 42° maximum.
For a 15-step, 1m-wide flight (180mm rise, 280mm going): the naive width × rise × going × steps formula gives 0.756 m³. The correct stacked-rectangle formula gives 6.048 m³ — the naive formula is 87.5% short. Ordering concrete from the wrong figure would leave a real pour badly incomplete.
Divide your total rise (floor-to-floor height) by a comfortable riser height, typically 175–180mm, and round to a whole number. A 2400mm rise at 175mm gives about 14 steps.
Around 175mm is a common comfortable default in Australia, within the 115–190mm NCC range for residential stairs. The exact figure depends on total rise and how evenly it divides into whole steps.
Around 250–280mm is comfortable for most adults, above the 240mm NCC minimum for Australian residential stairs. Deeper treads feel more spacious but use more floor space.
Take the arctangent of total rise divided by total run. A comfortable residential stair typically sits between 30° and 38°.
Twice the riser height plus the going should fall between roughly 550mm and 700mm in Australia and the UK (24–26 inches in the US) for a comfortable, safe walking rhythm. It catches combinations of rise and going that are each individually fine but awkward together.
190mm in Australia (NCC), 7¾ inches (196.85mm) in the US (IRC), and 220mm in the UK (Approved Document K, private stairs) — figures vary meaningfully by country, so use the right one for where the stair is being built.
240mm in Australia, 10 inches (254mm) in the US, and 220mm in the UK for private residential stairs.
Use the Pythagorean theorem: the square root of (total rise squared plus total run squared). Add roughly 150–300mm to the board you purchase beyond that calculated length, to allow for the top plumb cut and bottom seat cut.
This varies enormously by material, complexity and region. Enter your own material and labour rates into this calculator for a planning estimate, but get quotes from licensed builders for an accurate, binding price.
Simple, code-compliant timber stairs are within reach of a confident DIYer in many jurisdictions, but structural stairs, anything spanning between floors, or anything in a jurisdiction requiring certification should involve a licensed builder or engineer — and check whether a permit is needed before you start.
The NCC's own published guidance confirms there is no minimum stairway width specified for a Class 1 (house) or Class 10 (shed, deck) private stair. 600mm is the AS 1657 figure for industrial access stairs, not houses, and 1000mm applies only where a stair must be accessible under AS 1428.1. In the US, the IRC requires 36 inches (914.4mm) minimum. The UK's Approved Document K doesn't set a fixed minimum stair width directly, though other regulations like fire escape requirements may apply.
The same rise/run formula as any other stair — measure total rise from ground level to the deck surface, choose a comfortable riser height, and calculate as normal. Deck stairs often have a shorter total rise, so may only need 4–8 steps.
The angle of the staircase's slope, calculated as the arctangent of total rise divided by total run. The UK's Approved Document K caps private stair pitch at 42°.
The clear vertical space above the stair's nosing line — commonly required to be at least 2000mm in Australia and the UK, or 6'8" (2032mm) in the US. It's easy to design a stair that clears at the bottom of a flight but not partway up, so check it along the whole stair line.
A flat platform between flights of stairs, required once a flight exceeds a certain number of risers (commonly cited around 12–18 depending on the code) or where a stair changes direction. L-shaped, U-shaped and quarter-turn stairs all use a landing to join two shorter flights.
2 stringers for a narrow residential stair, 3 or more for wider stairs — roughly one every 900mm of width is a common guide, though check span tables for your specific timber and tread thickness.
Total stringer length (stringer length × number of stringers, plus waste allowance), plus one tread board per tread and one riser board per riser if using closed risers. This calculator works all of these out from your dimensions.
Divide total rise by a target riser height and round to a whole number of steps, then divide total rise by that step count for the actual uniform riser. Total run is the number of treads (one fewer than the steps) multiplied by the going.
The angled structural board that treads and risers are fixed to, running the full length of the stair from the bottom of the flight to the top. Timber stairs typically use 2–3 stringers depending on width.
Spiral stairs use different geometry from straight stairs — steps are calculated from total rise and an ideal riser height as normal, but going is measured at a walk line partway between the centre post and the outer edge, and the total turn (often 360°) is spread evenly across the steps. Spiral stairs are usually governed by a separate standard from straight-flight rules — always confirm with a specialist manufacturer or engineer.
Because a staircase is a stack of rectangles, not a uniform block — concrete under an upper step still has to fill all the way down to the ground. A simple width × rise × going × steps calculation can understate true volume by more than 80% on a typical flight.
Yes — the underlying rise/run geometry is identical. Outdoor and deck stairs just have extra practical considerations like drainage fall and slip resistance that this calculator doesn't specifically model.
This calculator flags it explicitly rather than hiding it — adjust your desired riser height (usually downward, adding a step) and recalculate, or confirm with your building surveyor if you believe a specific exception applies to your project.
No — each flight uses the same straight-stair formula. Calculate each flight of an L-shaped, U-shaped or quarter-turn stair separately using its own total rise, then add a landing between them.
10% is a reasonable default for both timber and concrete stairs, covering cutting losses and, for concrete, formwork that rarely pours to the exact calculated volume. Complex stairs may warrant more.