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Stair Calculator
Calculate whole riser count, equal actual riser height, tread count, total horizontal run, and basic stair proportion. The dedicated side elevation draws the calculated flight with rise and run dimensions for an immediate geometry check.
Number of risers-
Actual riser height-
Number of treads-
Estimated total run (m)-
Stair width (m)-
Straight-run plan footprint (m²)-
Total tread front-edge length (m)-
Decision view
Calculated stair rise and run
Calculated stair rise and runThe side elevation uses the whole riser and tread counts, labels equal actual riser height, and shows the resulting horizontal run.
Exact scenario comparisonTarget riser height (mm) changes while all other entered assumptions remain constant.
| Target riser height (mm) | Number of risers | Actual riser height | Number of treads | Estimated total run (m) | Stair width (m) | Straight-run plan footprint (m²) | Total tread front-edge length (m) |
|---|
How to use Stair Calculator
- Measure finished lower-floor to finished upper-floor elevation, including final floor build-ups.
- Enter a target riser and tread depth that are plausible under the applicable code and project constraints.
- Review actual equal riser height, total run, headroom, landings, support, nosing, handrails, and code with a qualified designer.
Calculator guide
Understanding Stair Calculator
A stair must divide the full floor-to-floor rise into equal risers while producing a practical horizontal run. This calculator shows that discrete geometry and highlights why changing the riser count changes every step.
Calculation method
How the calculation works
Round the riser count upward from total rise and target height, divide for an equal actual riser, calculate tread run, and use the entered width for straight-run footprint and tread-edge quantities. Divide total rise by target riser height and round upward to a whole riser count. Divide total rise by that count for equal actual risers, use one fewer tread for a simple floor-to-floor flight, and multiply treads by tread depth for total run.
Safety geometry
Equal risers matter more than matching the target exactly
The target guides the riser count; the final equal division controls the built flight.
Use the drawing as an early space and consistency check, never as fabrication or permit documentation.
Worked situations
Practical examples
- A 2,800 mm total rise divided by a 175 mm target produces exactly 16 risers.
- Sixteen risers create 15 treads in a simple flight between two finished floors.
- At 280 mm per tread, the basic horizontal run is 4.2 m before landings or nosing conventions.
Better inputs
Useful tips
- Recalculate after finished flooring thicknesses are confirmed; small level changes affect first and last risers.
- Check the entire flight for equal risers rather than adjusting one step in the field.
- Reserve space for landings, headroom, structure, guards, handrails, and circulation before fixing the opening.
Before relying on the result
Limitations and common mistakes
- The model is geometric and does not certify compliance with any building, accessibility, fire, or workplace code.
- Winders, spiral stairs, intermediate landings, nosing projection, stringer design, and headroom are not calculated.
- The simple tread count assumes a floor-to-floor flight where the upper finished floor acts as the final tread surface.
Reference
Key terms
- Total rise
- Vertical distance from one finished floor level to the next.
- Riser
- Vertical increment between consecutive tread surfaces.
- Tread depth
- Horizontal stepping depth defined by the applicable measurement convention.
- Total run
- Horizontal distance generated by all treads in the modeled flight.
Important note
Calculated from the entered measurements and stated coverage or quantity rules. Confirm field dimensions, waste, product requirements, structural conditions, and local codes before purchasing or building.
Frequently asked questions
Why is the riser count rounded up?
Rounding down would make each actual riser taller than the target, while rounding up keeps it at or below the entered target.
Why are there fewer treads than risers?
In a simple floor-to-floor flight, the upper finished floor serves as the final landing surface.
Does total run include nosings?
No. It multiplies the entered tread depth by tread count; code measurement conventions and nosing projection require separate review.
Can these dimensions be used for construction?
They are planning geometry only. Final stairs require field verification, structural design, detailed layout, and code approval.