Plan the risersActual riser = Total rise ÷ Riser countTreads = Riser count − 1
Enter total rise and your count or maximum. A maximum producing fewer than two risers gives a model-scope error, never a silent clamp.
FIELD TOOL / 015
Risers · Treads · Horizontal run
Transparent geometryStairs & structures
Stair Calculator
Plan one straight stair flight from your total rise, riser method and horizontal run. Uniform steps, transparent geometry.
Geometry only · No code approvalUnconfigured schematic — enter your flight measurements.
The upper floor/landing is the final stepping surface: treads = risers − 1. No intermediate landing or winders. Drawing capped at 12 treads for display only, not a construction limit. No stringer or cut layout is shown.
No black boxesUniform steps.
Uniform steps.
Visible equations.
One straight flight. The upper floor/landing is the final stepping surface, so the model has one fewer tread than risers. This is a geometry convention, not a code rule.
Plan the horizontal runTotal run = Unit run × Tread count
Each run method keeps its own physical input. No tread-board depth or nosing is inferred.
Repeating step pitchRatio = Actual riser ÷ Unit runAngle = atan(Ratio) × 180 ÷ π
Angle uses uniform step geometry, not total rise ÷ total run. N risers and N−1 treads describe different endpoint and repeating-step triangles.
All calculations use canonical full-precision values; display rounding never determines the flight. No stringer length is calculated.
Straight-flight geometry
How to use the Stair Calculator
Enter your finished total rise. Choose Number of risers or Your maximum riser height, then Unit run or Available total run. Every required field starts blank. Methods retain independent drafts, including on physical unit switches. A valid result describes one straight flight with uniform risers and horizontal unit runs, not an approved construction layout.
Straight-flight geometry
Total rise is a finished vertical height
Total rise is the modeled lower-to-upper floor/reference height. It must be positive. Inches and millimeters represent the same physical distance: 1 in = 25.4 mm. No floor thickness adjustment is inferred; enter the finished reference height required by your project.
Straight-flight geometry
Plan from your number of risers
For your intended whole count N, actual riser height = total rise ÷ N. This straight-flight model needs at least two risers, producing at least one stair tread. The count is obeyed exactly; the calculator does not search for an ideal stair or rank alternative layouts.
Straight-flight geometry
Plan from your maximum riser height
Enter a positive limit from your project specification or applicable requirements. Count = ceil(total rise ÷ your maximum), then actual riser = total rise ÷ count. The actual riser is at most your entered maximum, subject to floating-point tolerance. If the result has fewer than two risers, the model shows an error rather than silently forcing two. BuiltTally supplies no universal stair-code value.
Straight-flight geometry
Risers versus treads
Here the upper floor/landing acts as the final stepping surface. Therefore N risers correspond to N−1 stair treads: 15 risers means 14 treads. The final vertical rise reaches the upper surface. This is the calculator's explicit geometry convention, not a building-code rule or a universal layout for all stairs.
Straight-flight geometry
Unit run and available total run
Unit run is horizontal distance from one step reference line to the next, not tread-board depth or nosing projection. Unit mode gives total run = unit run × treads. Total mode gives unit run = entered available total run ÷ treads. Changing run never changes total rise, riser count or actual riser height. Changing count changes the derived run quantity while preserving the entered physical run.
Straight-flight geometry
Calculate repeating-step stair angle
Ratio = actual riser height ÷ unit run. Angle = atan(ratio), converted to degrees. Do not use total rise ÷ total run: this flight has N risers but N−1 treads, so its endpoint triangle differs from the repeating-step pitch. All calculations use unrounded canonical measurements.
Straight-flight geometry
What this calculator does not design
One straight flight only: no intermediate landing, winders, spiral or curved geometry. It does not calculate stringer length, stock, cuts, notches or connection details. Nosing, tread surface detailing, stair width, guard/handrail, headroom, loads and structural sizing are outside this model. A floor-to-floor diagonal does not resolve finished stringer stock or cutting geometry.
Straight-flight geometry
Project requirements remain separate
Calculated geometry is not a code, safety or buildability approval. Requirements vary by jurisdiction and project; verify applicable rules and specifications separately. No universal maximum riser, minimum run, angle, width, headroom, landing, railing or nosing value is supplied. Software length/count/ratio bounds and the drawing cap only protect numeric representation and rendering.
Hypothetical arithmetic only
Worked stair examples
Count + Unit Run: total rise 108 in, 15 risers and entered unit run 10 in. Actual riser = 108 ÷ 15 = 7.2 in. Treads = 15 − 1 = 14. Total run = 14 × 10 = 140 in. Step ratio = 7.2 ÷ 10 = 0.72; angle = atan(0.72) ≈ 35.7539°. The endpoint ratio 108 ÷ 140 is different and is not used for stair pitch.
Your maximum: hypothetical total rise 100 in and user-entered maximum 7.5 in. Count = ceil(100 ÷ 7.5) = 14; actual riser = 100 ÷ 14 ≈ 7.1429 in, with 13 treads.
108 in, 15 risers, 10 in unit run and 7.5 in maximum are arithmetic example inputs only. They are not recommendations, standards or code limits. Geometry only; verify applicable project/code requirements separately.
Common questions
Stair calculator FAQ
How do I calculate the number of stair risers?
Enter your intended whole count, or use your own maximum riser height with ceil(total rise ÷ maximum). This flight model needs at least two risers. No ideal count or code maximum is supplied.
Why are there fewer treads than risers in this model?
The upper floor/landing is the final stepping surface. Treads = risers − 1, so 15 risers means 14 stair treads. This is a stated geometric convention, not a code rule.
How is actual riser height calculated?
Total rise divided by the selected or derived riser count. Risers are uniform and the entered total rise is preserved.
How do I calculate total stair run?
In Unit Run mode, multiply horizontal unit run by tread count. In Total Available Run mode, retain the entered total run and divide by tread count to derive unit run.
What is unit run?
Horizontal distance from one step reference line to the next. It is not automatically tread-board depth or tread depth including nosing.
How is stair angle calculated?
atan(actual riser ÷ unit run), expressed in degrees. Total rise ÷ total run describes a different reference triangle for this N-riser/N−1-tread model.
Can I enter my own maximum riser height?
Yes. Use a limit from your project requirements, specification or applicable rules. BuiltTally does not provide a universal code value; fewer than two derived risers produces a model-scope error.
Does this calculator check building code?
No. BuiltTally calculates the geometry you enter. Stair requirements vary by jurisdiction and project. Verify applicable requirements separately.
Does this calculate stringer length?
No. Finished stringer layout can depend on connections, stock, top/bottom cuts, notches, floor/landing details and other construction choices. This tool provides uniform rise/run geometry without a misleading diagonal shortcut.
Does it include nosing?
No. Tread-board depth and nosing projection are separate detailing issues, outside this phase.
Can it calculate stairs with a landing or winders?
No. This model is one straight flight with uniform steps and no intermediate landing, winders, spiral or curved geometry.