Stair Calculator
Adjust the inputs below. Results update as you type.
How it works
IRC code: max rise 7¾ inches, min run 10 inches, min width 36 inches. Total rise / number of risers = rise per step. Number of risers = total rise / desired rise (round to nearest integer). Run × (risers − 1) = horizontal run. Stringer length = √(total rise² + total run²). Comfortable ratio: 2 × rise + run = 24–25 inches. Consistent rise height is critical for safety.
Input guidance
- Confirm date/time/unit settings before comparing outputs.
- If a task has optional fields, run both with and without them to understand impact.
- Save scenario variants when making practical decisions.
The formula
Number of steps = total rise ÷ ideal riser height (about 7 inches). Tread depth and riser should satisfy comfort rules like riser + tread ≈ 17–18 inches.
Worked example
A total rise of 112 inches ÷ 7-inch risers = 16 risers, with treads around 10–11 inches deep for a comfortable, code-friendly stair.
More examples to test
- Quick-pass example: run default assumptions for a first estimate.
- Refined example: update one assumption at a time to isolate impact.
How to interpret results
Use outputs as operational estimates and pair them with local constraints, business rules, or provider requirements.
When this can be inaccurate
Utilities can miss local policy details, special-case rules, and environment-specific constraints.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Find productivity tools for everyday workflows
General recommendation, not professional advice.
Frequently asked questions
What is a comfortable stair ratio?+
A common rule keeps riser plus tread near 17–18 inches, with risers around 7 inches and treads about 10–11 inches.
How many steps do I need?+
Divide the total floor-to-floor rise by the target riser height and round to a whole number, then recompute the exact riser.
Are there building code limits?+
Yes. Local codes set maximum riser and minimum tread dimensions for safety, so check requirements before building.
Why are outputs slightly different from another tool?+
Different tools can use different rounding rules, default assumptions, and treatment of edge cases.
How can I improve estimate reliability?+
Use verified inputs from real records and re-run calculations after major assumption changes.