What this calculator actually models
Stair geometry starts from total vertical rise and total horizontal run. Once you choose a riser count, the calculator divides the rise equally and treats a typical straight flight as one fewer tread than risers for geometric planning.
How to use this calculator
Enter total floor-to-floor rise and total horizontal run using the same unit.
Enter the number of risers you want to evaluate.
Review equal riser height, tread depth, tread count, straight slope length and angle, then compare against the requirements that apply to the actual stair.
Where people use it
- •Early straight-stair layout checks
- •Comparing riser-count options
- •Drawing and fabrication geometry
Example: 105 in rise, 132 in run, 15 risers
Fifteen risers produce 7 in per riser. Fourteen tread intervals across 132 in produce about 9.43 in per tread before nosing, finishes or code-specific definitions.
Assumptions and limits
- •This page calculates geometry only and does not determine whether a stair complies with building code, accessibility rules, headroom, landing, nosing, handrail or structural requirements.
- •Real stair layout must use the governing code and field dimensions, including finished-floor thickness and framing details.
Frequently asked questions
Why are there usually fewer treads than risers?+
In a common straight stair between two floor levels, the upper floor acts as the final landing, so geometric tread intervals are often one fewer than the riser count.
Does this tell me whether my stair is code compliant?+
No. It deliberately avoids universal code claims because requirements vary by jurisdiction and stair type.
Can I use millimeters instead of inches?+
Yes. Use any single length unit consistently for total rise and run; the returned riser, tread and stringer lengths use that same unit.
Semantic next steps
Continue the calculation
These links move to a different input, formula or project stage rather than a keyword variation of this page.
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