Stair Stringer Calculator (Risers, Treads & Stringer Length)
Number of risers and treads, exact riser height, total run and stringer length from the floor-to-floor rise, checked against the IRC 7¾ in maximum riser.
Formula
Risers = ⌈total rise ÷ max riser⌉; riser height = total rise ÷ risers; treads = risers − 1; total run = treads × tread depth; stringer length = √(rise² + run²).
Worked example
Inputs: Total rise (finished floor to finished floor) = 108 in; Maximum riser height allowed = 7.75 in; Tread depth (run per step) = 10 in.
| Risers | 14 |
|---|---|
| Riser height in | 7.714 |
| Treads | 13 |
| Total run in | 130 |
| Stringer length in | 169.01 |
| Stringer length ft | 14.08 |
| Stair angle deg | 39.7 |
FAQ
What are the code limits for residential stairs?
The 2021 IRC (R311.7.5) sets a maximum riser height of 7¾ in and a minimum tread depth of 10 in. Your local jurisdiction may amend these, so confirm with the building department.
Why is there one fewer tread than risers?
The top riser lands on the upper floor, so a straight run of n risers has n − 1 treads.
Is stringer length the board length to buy?
No. It is the diagonal along the stair line. Buy a longer board (often a 2×12) to allow for the top and bottom cuts and any landing connection.
Sources
- ICC 2021 International Residential Code, Chapter 3, Section R311.7 (stairways: max riser 7¾ in, min tread 10 in)
- Geometry (volume/area formulas); no external constant needed
Related
- Rafter Length Calculator (From Run and Roof Pitch)
- Wall Stud Calculator (Studs & Plates for a Framed Wall)
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Last reviewed 2026-10-13.