Stairs calculator
Stair Calculator
Divide total rise into equal risers near the target height, verify the entered maximum, then calculate tread count, total run, stringer slope length, and stair angle.
Planning estimate, not a contractor quote. Review the assumptions and replace presets with local prices when available.
Method
How this calculator works
Safe stair layout starts with an accurate finished-floor-to-finished-floor rise. The risers must be equal, so the final riser height is the total rise divided by a whole number—not simply the target entered. Code adoption and field conditions vary, so this calculator reports geometry and planning checks rather than declaring compliance.
Risers = a whole number near total rise ÷ target riser, increased if needed to stay under the entered maximum. Riser height = total rise ÷ risers. With the upper floor as the final tread, treads = risers − 1. Run = treads × tread depth. Stringer slope = √(rise² + run²).
Worked example
A realistic starting point
A 105 in total rise with a 7 in target produces 15 risers at exactly 7 in. With the upper floor as the final tread, there are 14 treads at 11 in for 154 in of run, a 186.39 in slope length, and a 34.29° angle.
What changes the answer
Factors worth checking
Finished-floor rise
Measure after accounting for finished flooring at both levels. Small errors become visible across every riser.
Tread and nosing
Code definitions distinguish tread depth, nosing, and riser geometry. Use the project’s applicable definition and detail.
Landings and headroom
Total run must fit while maintaining required landings, headroom, clear width, guards, and handrails.
Stringer structure
Slope length is not a structural sizing result. Material species, cuts, span, support, loads, and connections need proper design.
Common questions
Stairs FAQ
Why are there usually fewer treads than risers?
When the upper floor is the final walking surface, the last rise reaches that floor, so a straight flight has one fewer constructed tread than risers.
Does the calculator guarantee code compliance?
No. Local adoption, amendments, occupancy, construction type, and field details control. Treat the checks as planning information.
What is the 2R + T rule?
It is a comfort heuristic using twice the riser height plus tread depth, often compared with a 24–26 in range. It is not a replacement for code.
Can I size a stringer from this result?
The slope length helps with layout, but stringer member size, notching, span, support, species, loads, and connections require structural judgment.
Evidence
Sources & review
- International Residential Code — Building PlanningBaseline residential stair provisions; verify the locally adopted code and amendments.
Published by Calcstead. Report a correction.
Method and source links reviewed September 4, 2026. Price presets are editable planning inputs and should be replaced with current local information.