Formula and input notes
Risers = ceil(total rise ÷ target riser); actual riser = total rise ÷ risers; total run = (risers − 1) × tread depth
| Input | Practical note |
|---|---|
| Target riser height | This is a planning target used only to choose a whole riser count; the calculator then recomputes the equal actual riser height. |
| Tread depth | This is the horizontal depth assigned to each tread in the run calculation; confirm how nosing is treated in the governing layout convention. |
Worked stair example
Stair Calculator example: ceil(121 in ÷ 7.25 in) = 17 risers. Each actual riser is 7.12 in; 16 treads at 10 in create 160 in of run and a 200.6-in diagonal.
Use the whole-riser layout
Use the whole-riser result to develop a full stair drawing; never round each riser independently, because small differences accumulate over the flight.
Code and construction checks still required
Finished floor thickness, landing arrangement, nosing, headroom, stringer bearing, tread count convention, and rounding to whole risers affect layout.
Questions specific to this calculation
Why does actual riser height change after calculation?
A flight needs a whole number of equal risers. The calculator rounds the count up from total rise divided by target height, then divides the same total rise by that whole count to produce the actual riser.
How are tread count, total run, and stringer length related?
For the displayed straight-flight convention, tread count is one less than riser count. Total run is that tread count times tread depth, and stringer line length is the hypotenuse formed by total rise and total run.
Does the stair result establish code compliance?
No. Verify allowable riser and tread dimensions, variation, nosing, width, headroom, landings, guards, handrails, and structural details with the code and authority governing the project.