Stair Rise & Run Limits for the Stair Stringer Layout Tool
Use this table next to numbers from the stair stringer layout tool. Every row is a hint, not a certification. The IRC text, local amendments, and the person who stamps the job outrank this page.
| Topic | Common figure (in) | Common figure (mm) | How to read it |
|---|---|---|---|
| Maximum riser height | 7.75 in | 197 mm | Common IRC residential figure. Hints only. |
| Minimum tread depth (nosing to nosing) | 10 in | 254 mm | Common IRC residential figure. Hints only. |
| Maximum variation between risers or treads | 3/8 in | 9.5 mm | Keep cuts consistent. Hints only. |
| Minimum stair width | 36 in | 914 mm | Clear width between finish surfaces. Hints only. |
| Minimum headroom | 6 ft 8 in | 2032 mm | Measured plumb from the tread nosing line. Hints only. |
| Throat remaining (shop hint) | 3.5 in | 89 mm | Not an IRC table value. Some framers prefer about 5 in on long spans. Hints only. |
How the tool picks riser count
In total-run mode the calculator takes max(2, round(total rise / 7.5 in)), or
190 mm in metric, then divides the finished rise evenly. Tread-count mode sets
risers = treads + 1 instead. Equal finished rises matter more than hitting 7.5 in exactly.
Questions
Does this stair stringer layout tool pass or fail my stairs?
No. The table is a set of commonly cited IRC residential figures plus one shop hint for throat. Local amendments, inspector practice, and a qualified professional decide what you may build.
Why does the calculator sometimes show a riser over 7.75 in?
Riser count is chosen by rounding total rise to a 7.5 in (or 190 mm) target. That can land a hair over a cited maximum. Change rise, add a riser by using tread-count mode, or treat the number as a prompt to restudy the landing, not as a verdict.
What throat should I keep on a 2x12?
Carpentry references disagree. This page shows 3.5 in as a conservative shop hint and notes that 5 in is also used. Recalculate on 2x14 if the tool throat looks skinny.
For reference only. Construction must follow local code and a qualified professional. This table does not judge compliance and does not size stringers for load.