Stair Stringer Calculator
Turn a total rise into riser count and height, tread run, total run, and stringer length, with code flags.
Processed locally in your browser — nothing is uploaded.
Stair Stringer Calculator
Finished floor to finished floor, measured plumb
IRC residential code max is 7-3/4 in
10–11 in typical; IRC minimum is 10 in
Enter the total rise to lay out the stringer.
About Stair Stringer Calculator
Enter the total rise and the tool divides it by the maximum riser height (7-3/4 in, the IRC residential limit, editable) to get the riser count, then computes the exact equal riser height, tread count, total run at your tread depth, and the diagonal stringer length. Risers outside the 4–7.75 in code range are flagged.
Common uses
- Lay out a deck stair stringer from a measured rise
- Check whether a basement stair can fit its run
Example
Input
100 in total rise, 7.75 in max riser, 10.5 in treads
Output
13 risers of 7.69 in · 12 treads · 126 in run · 161 in stringer
Limitations
- Local codes differ on riser/tread limits, nosing, and headroom — verify before cutting
- Assumes the top tread is the upper floor (risers = treads + 1)
Frequently asked questions
How many steps do I need for a 36 inch deck?
Five risers of 7.2 in each and four treads. At 10.5 in treads that's 42 in of total run and a stringer 55.3 in long — the diagonal of the 36 in rise and 42 in run.
What is the maximum riser height allowed by code?
7-3/4 in for residential stairs under the IRC, with a 10 in minimum tread depth; this calculator defaults to that limit and flags any riser outside the 4–7.75 in range. Risers within one flight also can't vary by more than 3/8 in, which is why the tool divides the rise into exactly equal risers rather than leaving a short step at the bottom.
Why is there one more riser than tread?
The top riser lands on the upper floor or deck surface, so that floor acts as the last tread. Treads always come out one fewer than risers on a straight run — which is what this calculator assumes.
How long a board do I need to cut a stair stringer?
At least the diagonal length √(rise² + run²): a 100 in rise with a 126 in run needs 161 in, or 13.4 ft, so you'd buy 14 or 16 ft stock. Cut stringers are normally laid out on 2x12, since notching the treads and risers eats most of the board's width.
Does this calculator send my stair measurements anywhere?
No. The riser, tread, and stringer math runs in your browser — the rise you measure and the results are never transmitted or stored.