Stair geometry from your total floor-to-floor rise: number of risers, the actual riser height you end up with, treads, total run, pitch angle and the 2R+T comfort check. Geometry for planning — stair regulations vary by country, and structural stairs need a professional.
How to Use the Stair Calculator
Everything starts from the total rise, and the total rise is finished floor to finished floor — the vertical distance from the surface you step off at the bottom to the surface you arrive at on top. That means both floor build-ups count: boards, screed, tile. Measuring floor to ceiling, or to the joists, produces stairs that miss the landing by the thickness of the flooring, which is the single most common stair-plotting error. If the two floors have different build-ups, measure the actual finished surfaces.
The riser you want and the riser you get are different numbers, and the calculator is honest about it. Divide the total rise by your desired riser and you almost never get a whole number — 270 cm at a 17.5 cm target is 15.43 risers, and nobody builds 0.43 of a riser. The calculator rounds to the nearest whole count (15) and reports the actual riser you will cut: 270 ÷ 15 = 18 cm exactly. Uniform risers matter more than the target number itself — a stair with one odd riser is a stair people trip on, typically at the top where the body has stopped paying attention.
Treads are risers minus one, and the reason is geometry: the top riser lands flush with the upper floor, so the floor itself is the final tread. A 15-riser stair has 14 framed treads. The going — the horizontal depth of each tread, measured nosing to nosing where a nosing exists — multiplies out to the total run, the floor space the stair consumes before landings or turns.
What feels comfortable is remarkably consistent across people, which is where the 2R+T rule comes from: twice the riser plus the going should land around 600–640 mm (24–25 in). It is a comfort rule of thumb, not a regulation. A typical domestic stair works with risers around 170–180 mm and goings around 250–300 mm; commonly seen ranges for homes run wider — roughly 125–190 mm risers and 250–320 mm goings — because utility stairs, compact secondary stairs and grand primary stairs all push the extremes. Pitch follows the same logic: most main domestic stairs sit between about 30° and 38°; steeper saves floor area but climbs harder.
Two numbers this tool deliberately does not compute: headroom and stair width. Headroom — the clear vertical allowance above the nosing line — is commonly around 2000 mm minimum in many jurisdictions, but the figure and how it is measured vary. Width for a main domestic stair is commonly around 900–1000 mm. Both are regulated, both interact with the landings and the structure around the stair, and both are reasons to read the stair dimension guide before committing to a layout.
The Math Behind the Calculator
Four lines of arithmetic and one inverse tangent. The only subtlety is the rounding of the riser count — round to the nearest integer, then let the actual riser height absorb the remainder.
risers = round(total_rise ÷ desired_riser)
actual_riser = total_rise ÷ risers
treads = risers − 1
total_run = treads × tread ÷ 100 (cm → m)
angle = atan(actual_riser ÷ tread)
comfort = 2 × actual_riser + tread (aim 600–640 mm)
Every comfort range quoted — 600–640 mm for 2R+T, roughly 125–190 mm risers, 250–320 mm goings, 30–38° pitch — is a typical range for planning, not a standard. Regulated limits differ by country, state and building type, and they are not always symmetrical: some jurisdictions set maximum risers far below 190 mm for certain stair types. Verify against your local rules before cutting anything.
Worked Example: 270 cm Floor-to-Floor
A stair between two floors 270 cm apart (finished to finished), with a 17.5 cm target riser and a 28 cm going. Enter rise 270, riser 17.5, tread 28.
- Riser count: 270 ÷ 17.5 = 15.43 → rounds to 15 risers.
- Actual riser: 270 ÷ 15 = 18.0 cm — slightly taller than the target, still well inside the typical range.
- Treads: 15 − 1 = 14 framed treads.
- Total run: 14 × 0.28 = 3.92 m of horizontal floor space.
- Pitch angle: atan(18 ÷ 28) = atan(0.643) ≈ 32.7° — a comfortable main-stair pitch.
- Comfort check: 2 × 18 + 28 = 64 cm — comfortable, right at the top of the band.
Now watch the alternative. Prefer a shallower riser? 16 risers give 270 ÷ 16 = 16.875 cm ≈ 16.9 cm each, 15 treads, a run of 15 × 0.28 = 4.2 m, a pitch of atan(16.875 ÷ 28) ≈ 31.1°, and 2R+T = 2 × 16.875 + 28 = 61.75 cm — more comfortable still, but 28 cm deeper into the floor plan. That is the constant trade in stair design: every millimetre of gentleness is paid for in run, and every millimetre of compactness is paid for in steepness.
If the run does not fit the space, the standard moves are a mid-stair landing with a 90° or 180° turn, or winder treads at the corner — both of which change the footprint calculations and are exactly where regulations bite hardest. Plan the geometry here, then check the layout against the rules that apply where you are building.
Safety & Regulations
Reminder
Stairs are among the most regulated parts of a building, and the rules vary by country, state and even by building type. Limits on riser height, going, uniformity, headroom, handrails, landings and guarding all differ by jurisdiction, and none of them are checked by this calculator. This tool computes geometry for planning and roughing-out only — it is not a code compliance check and cannot approve a design. Structural stairs — cut stringers, connections, anything spanning between floors — carry people and loads, and designing and building them needs a qualified professional: a licensed builder or structural engineer working to your local regulations. If anyone other than you will use the stair, that is not the place to learn.
Assumptions & Limitations
Every number above rests on these constants. If your project differs, change the matching input — or read the linked guide for the full reasoning.
- Total rise is finished-floor to finished-floor, including both floor build-ups
- Riser count rounds to the nearest whole number; the actual riser height absorbs the remainder
- Comfort bands — 2R+T of 600–640 mm, risers roughly 125–190 mm, goings roughly 250–320 mm, pitch 30–38° — are typical ranges, not regulations
- Verdicts (Comfortable / Steep / Shallow) judge geometry against the comfort band only
- No headroom, width, handrail, landing or guarding checks — and no structural design whatsoever