PROFESSIONAL STAIR GEOMETRY
Solve risers, going, pitch, run, stringers, headroom checks and timber quantities.
BUILD MEASURE HELPER
Calculation summary
Planning estimate only. Verify product specifications, site conditions and purchase quantities before ordering.
DIY complexity
Stair geometry is safety-critical and tightly regulated — inconsistent riser heights are a leading cause of falls, and most jurisdictions require the finished stair to meet code, which is difficult to guarantee without professional experience.
This calculator turns a single master dimension — the finished floor-to-floor total rise, not the rough framed opening — into a full stair layout: whole-number riser count, actual riser height, going (tread depth) from a widely used comfort formula, total run, and quantities for stringers, treads, risers and handrails. Because a real staircase cannot have a fractional step, the total rise is always divided into a whole number of equal risers, and that whole number is what actually determines the riser height you build to, not the target riser you typed in. The going is then derived from that actual riser using a comfort rule of thumb that balances riser and going so the stair feels neither cramped nor stretched to walk. The tool also reports headroom along the stair line and flags how many stringers and which handrail configuration (one or both sides) the width and rise suggest. It is built for straight residential and light-commercial staircases — indoor, outdoor, garden or loft-access — and it deliberately keeps geometry separate from local law: minimum and maximum riser and going dimensions, headroom clearance and handrail requirements are set by building codes that differ by country and sometimes by region, and this calculator's comfort formula is a design aid, not a substitute for checking those rules before you build.
Quick answer
For a 2.8 m total floor-to-floor rise with a 175 mm target riser, the stair needs 16 equal risers (round(2800 ÷ 175) = 16), each exactly 175 mm high, with a comfort-formula going of about 280 mm (630 − 2 × 175) and a total run of 15 × 280 mm = 4.2 m — before checking that figure against local minimum/maximum going rules.
risers = round(total_rise ÷ target_riser)The total rise is divided by the target riser height and rounded to the nearest whole number, because a staircase must always have a whole number of steps — you cannot build 15.6 risers.
Rounding rule: Rounded to the nearest whole number (not floor or ceiling) so the resulting actual riser stays as close as possible to your target in either direction.
Limitation: Rounding to a whole riser count means the actual riser height you build to is virtually never exactly the target you typed — this is expected behaviour, not an error, and the actual figure is what must be checked against code limits.
actual_riser = total_rise ÷ risers · going ≈ 630 mm − 2 × actual_riserThe actual riser is recalculated from the whole riser count, then a widely used comfort rule of thumb — twice the riser plus the going equals roughly 630 mm — is rearranged to suggest a comfortable going for that specific riser height. A shorter riser suggests a deeper going, and a taller riser suggests a shallower one.
Rounding rule: The going suggestion is typically rounded to the nearest 5 or 10 mm (or nearest 1/4 in) for buildability, then compared against the entered minimum and maximum going range.
Limitation: This is a comfort rule of thumb, not a universal constant or a legal requirement — different countries define their own minimum and maximum riser and going dimensions, and some use a different comfort constant entirely; always verify against the applicable local building code.
total_run = going × (risers − 1)The horizontal length the stair occupies on plan is the going multiplied by the number of goings, which is always one fewer than the number of risers, because the top landing itself does not add a going.
Rounding rule: Computed from the already-rounded going and whole riser count, then displayed to the nearest 10 mm or nearest 1/8 in.
Limitation: Assumes a single straight flight; a stair with a landing, winders or a turn needs each straight section measured and totalled separately, since total_run only describes one uninterrupted run.
A straight indoor staircase between two finished floors 2.8 m apart, 1 m wide, with a 175 mm target riser and no unusual going constraints entered.
risers = round(2800 ÷ 175) = 16. actual_riser = 2800 ÷ 16 = 175 mm. going ≈ 630 − 2 × 175 = 280 mm. total_run = 280 × (16 − 1) = 4200 mm = 4.2 m.
Because 2800 divides evenly by 175, the target and actual riser match exactly in this case — that will not always happen. 4.2 m of total run is the horizontal space to reserve on the floor plan before adding any landing.
⚠ This exact match between target and actual riser is a coincidence of the numbers chosen, not something the calculator guarantees — always read the actual riser and going the tool reports, not the value you typed in.
A short garden stair down to a patio: 0.52 m total rise, 0.9 m wide, target riser 173 mm, 3 stringers for the wider run, minimum going 280 mm and maximum going 340 mm entered, 25 mm nosing.
risers = round(520 ÷ 173) = round(3.006) = 3. actual_riser = 520 ÷ 3 = 173.3 mm. going ≈ 630 − 2 × 173.3 = 283.3 mm, rounded to 285 mm — within the 280–340 mm entered range. total_run = 285 × (3 − 1) = 570 mm.
With only 3 risers, this stair is short enough that the comfort going comfortably clears the minimum going limit with room to spare; the third stringer is recommended purely because of the 0.9 m width, not because of the rise.
⚠ For very short flights like this one, always double-check that the actual riser and going still satisfy local outdoor-stair rules, which are sometimes stricter than indoor rules because of weather and slip risk.
A narrow 0.8 m wide loft-conversion stair, 2.6 m total rise, target riser 200 mm, 2 stringers, entered local prices of €45 per stringer, €18 per tread and €9 per riser board.
risers = round(2600 ÷ 200) = 13. actual_riser = 2600 ÷ 13 = 200 mm exactly. going ≈ 630 − 2 × 200 = 230 mm. total_run = 230 × 12 = 2760 mm = 2.76 m. Material cost: 2 stringers × €45 = €90, 13 treads × €18 = €234, 13 riser boards × €9 = €117; subtotal = €90 + €234 + €117 = €441.
€441 covers only stringers, treads and riser boards at the entered unit prices — fixings, handrail, balustrade, finish and labour are separate line items not included in this subtotal, so treat it as a materials-only starting point.
⚠ A width of 0.8 m and 13 risers over 2.6 m is steep and narrow enough that many building codes restrict or disallow this exact configuration for a primary staircase — confirm minimum width, maximum riser and headroom rules for loft or attic access stairs specifically before ordering material.
The result panel distinguishes the target riser you entered from the actual riser the calculator built to, because these are almost never identical once whole-number rounding is applied — the actual figure is the one to build from and check against code. Going, total run and headroom are shown as consequences of that actual riser, not independent inputs, so changing the target riser cascades through all of them. Stringer, tread, riser-board and handrail quantities are listed separately because they follow different unit-purchase logic than the geometry above them, and any entered price is totalled only from the material line items you priced, not including fixings, finish or labour unless you added those yourself.
Riser and going limits, headroom clearance, handrail height and guard requirements differ by country and often by stair use (primary staircase versus loft or attic access versus outdoor step), so always enter the minimum and maximum going that applies to your specific project rather than a generic default. Metric markets typically size stringers, treads and riser boards in millimetres and centimetres; imperial markets commonly use inches for riser and going. Timber, concrete, steel and stone stair construction each have their own supplier sizing conventions and fixing methods, so use dimensions and prices from the selected product or fabricator rather than assuming one material's defaults apply to another. Selecting a different currency only changes the displayed symbol — enter a current local price for stringers, treads, riser boards, handrail and any balustrade to get a realistic materials estimate, and confirm applicable sales tax and installation labour separately since neither is built into the calculator's output.
This calculator produces a planning-level stair geometry estimate using a general comfort formula — it is not a substitute for your local building code's stair regulations, and it does not check structural loading, fire escape width requirements, accessibility standards, or site-specific conditions such as sloped floors or out-of-square walls. Minimum and maximum riser and going, required headroom, handrail height, guard-rail triggers and winder or landing rules for turning stairs all vary by country and often by region or stair use, and must be verified against the applicable code before construction begins. It also assumes a single straight flight; stairs with landings, winders or turns must be measured and calculated section by section. Always confirm final dimensions on site and with a qualified professional before cutting stringers or ordering material.
Last reviewed: 2026-08-25
A staircase must have a whole number of equal steps — you cannot build a fractional riser — so the total rise is always divided by the target riser and rounded to the nearest whole number.
Because the riser count was rounded to a whole number, the total rise divided by that whole number is almost never exactly your original target — the actual value is the one the stair is truly built to.
No. It is a widely used design rule of thumb for balancing riser and going comfort, not a universal building-code constant — treat the resulting going as a suggestion to check against your local minimum and maximum going limits.
The rough opening is the unfinished structural gap in the floor framing; the total rise is measured between finished floor surfaces, after flooring and any subfloor build-up, and is the correct figure to enter here.
No. It computes geometry from the comfort formula and the limits you enter, but minimum and maximum riser and going, headroom clearance and handrail rules are set by codes that vary by country and sometimes region, and must be verified separately.
Stringer count generally increases with stair width and load, with a middle stringer commonly added on wider flights — enter your width and treat the suggested count as a starting point to confirm against local structural practice.
No, the going is still measured from one riser's face to the next; nosing simply lets the tread overhang the riser below, adding usable foot space without altering the going dimension itself.
It calculates one straight flight at a time. For a dog-leg, quarter-turn or stair with a landing, calculate each straight section separately and add its rise, run and stringer/tread quantities to the others.