Interactive Stair calculator
Estimated result
Enter measurements and select Calculate.
How to use this calculator
- Measure finished-floor to finished-floor total rise.
- Enter a planning riser target and tread depth.
- Optionally enter available horizontal run.
- Verify the resulting layout against the exact locally adopted rules and professional requirements before construction.
Formula and method
Risers = round up(total rise ÷ target riser). Actual riser = total rise ÷ risers. Treads = risers − 1. Run = treads × tread depth. Stringer = √(rise² + run²).
Worked example
For a 108 in total rise with a 7.5 in planning target, the tool selects 15 risers at 7.2 in each, 14 treads, and calculates run from the entered tread depth.
Assumptions and result interpretation
- The stair is a straight flight with uniform risers and treads.
- The tool does not model landings, winders, nosings, headroom, guards, handrails, structure, or finish buildup.
- Building requirements vary by jurisdiction; a result is not a code-compliance determination.
Common mistakes
- Measuring before finished floor thickness is known
- Using a different unit for rise and tread without selecting it
- Calling a mathematical fit code compliant
- Forgetting that a stair with N risers normally has N−1 treads to the upper floor
Methodology sources
Conversions use deterministic factors. Variable material properties are either visibly sourced and editable or left for the user to enter from the supplier.
Results are planning estimates. Confirm actual requirements with the appropriate supplier, contractor, engineer, building official, or other qualified professional.