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Stair Calculator

Updated Aug 24, 2026 Reviewed Aug 24, 2026

Calculate equal risers, treads, run, angle, stringer length, surface quantities, space differences, and approximate floor opening.

Straight-flight stair geometry

Enter rise, treads, space, and reference values

Input dimension unit

Finished-floor total rise

Measure lower finished floor to upper finished floor.

Target maximum riser height

The equal result will not exceed this target.

Tread depth / run per step

Stair width

Available horizontal run

Optional; enter it to compare with available space.

Finish quantities

Nosing depth

Tread finish thickness

Approximate headroom opening

Estimate required horizontal floor opening

Uses uniform slope, reference headroom, and floor thickness.

Upper floor thickness

Reference headroom

Available floor-opening length

Optional; enter it to compare with available space.

This is geometric only. Beams, landings, finishes, framing, and local measurement rules can change it.

Editable dimensional references

Replace defaults with locally adopted requirements

Defaults are selected 2021 IRC dimensional references. A passing check is not compliance or safety approval.

Reference maximum riser

Reference minimum tread

Reference minimum width

Result length unit

Geometry reference only

Does not design stringers, landings, guards, handrails, connections, framing, fire protection, accessibility, or complete compliance.

Result

Calculation summary

Enter values to see the result

Your result, breakdown, assumptions, and warnings will appear here.

Straight-flight preview

Equal risers and uniform treads

Live preview

The schematic updates from calculated equal-riser geometry.

How to use this calculator

1Enter total rise and select target-height or fixed-count mode.
2Enter tread, width, finishes, and optional available space.
3Replace all reference values with locally adopted requirements.

Formula

Risers = ceil(rise ÷ target); riser = rise ÷ risers; run = (risers − 1) × tread

A straight uniform flight has one fewer constructed tread than risers when the upper floor is final.

Calculation steps

Normalize dimensions.
Choose whole riser count.
Calculate equal rise and run.
Calculate angle, diagonal, and surfaces.
Compare space and references.
Approximate opening when enabled.

Worked example

A 280 cm rise with an 18 cm target gives 16 risers at 17.5 cm and fifteen 28 cm treads for a 420 cm run.

Assumptions

One straight uniform flight.
Checks never certify compliance.
Defaults are selected 2021 IRC dimensions.
Opening is approximate.
Structure, connections, guards, handrails, landings, and loads are outside scope.

Sources

Frequently asked questions

Why fewer treads than risers?

The upper floor is the final surface, so 16 risers normally mean 15 constructed treads.

Does green mean code compliant?

No. It compares one dimension with a value you entered.

How is opening estimated?

Headroom plus floor thickness is projected horizontally along the stair slope.

Can it design a landing or turn?

No. Model straight flights separately and review the complete arrangement.

Does stringer length include extensions?

No. It is the geometric diagonal only.

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