Stair Calculator
Estimate rise, run, step pitch and stringer reference lengths.
Your project
Enter your measurements. Required fields are labeled; assumptions and optional quotes can be edited below.
Loading measurement inputs…
How this calculator works
Measure the total finished rise from the lower floor to the upper landing. Enter a desired upper target riser and horizontal nosing-to-nosing going; going is not tread-board width. An optional available straight run excludes landing allowances. This is one straight flight of uniform risers. The upper landing supplies the final walking surface, so the flight has one fewer tread/going than risers.
H = total rise; T = going; n = max(2, ceil(H / target riser)); actual riser r = H / n; treads q = n − 1; horizontal run R = q × T; repeated-step pitch θ = atan(r / T) × 180 / π.The ceiling-to-target model keeps actual risers at or below the selected target within numerical tolerance. At least two risers are retained even when total rise is no greater than the target, with a low-rise/single-step review warning. At most 100 risers are supported. If available run is shorter than the calculated run, the result remains visible with the geometric shortage; going is never silently changed to force a fit. Otherwise the result may show spare geometric run. Neither state is a design approval.
Stringer reference — overall rise/run diagonal: endpoints (0,0) to (R,H), length hypot(R,H). Step pitch-line length: first tread nosing (0,r) to upper landing nosing (R,H), length hypot(R,H−r) = q × hypot(T,r). The pitch line angle equals repeated-step pitch. The gross diagonal angle atan(H/R) differs because q = n − 1; it must not be substituted for step pitch. These reference lines are distinct and are never combined into a physical stringer length.
Assumptions and limitations
Geometry planning only. Verify local rules and have the complete stair design checked before cutting or building. Reference geometry only; actual stringer stock and cuts depend on tread/riser thickness, attachment, bearing and layout details. No code compliance, structural adequacy, stringer stock size, physical cut length or cut template is supplied. No intermediate landings, multiple flights, winders, spirals, tread/riser-board takeoff or jurisdiction-specific pass/fail model is included.
US/Metric changes representation only, including inactive fields. Explicit US-market and Metric-market presets change their listed assumptions, never project measurements. Assumptions are editable planning inputs. Required project measurements start blank; calculate explicitly before valid edits update the estimate.
Worked examples
STAIRS-01: Total rise 108 in (9 ft), target 7 in, going 10 in and available run 144 in (12 ft). Result: 16 risers, actual riser 6.75 in, 15 treads, total run 150 in, repeated-step pitch 34.01934998982646° and run shortage 6 in. Overall rise/run diagonal reference is 184.8350616090 in; step pitch-line length is 180.9739276802 in. Neither is an approved cut length.
STAIRS-02: Total rise 2.8 m, target 180 mm, going 280 mm and available run 4.3 m. Result: 16 risers, actual riser 175 mm, 15 treads, total run 4.2 m, repeated-step pitch 32.005383208083494° and spare run 0.1 m. Overall diagonal reference is 5.0477717856 m; step pitch-line length is 4.9528400943 m. Both are reference geometry only.
Review the complete geometry, applicable rules, attachment, bearing and actual construction details with the person responsible for the stair design. This calculator has no material cost.