Stair Calculator
Turn a floor-to-floor rise into a full stair layout — step count, riser height, tread depth, and stringer length — with a code check.
How it works
Start with the total rise, the vertical distance from the lower finished floor to the upper one. The calculator divides that by a comfortable target riser of about 7 inches, rounds to a whole number of steps, then splits the rise back out evenly so every riser is exactly the same height.
Tread depth comes next. If you know the total horizontal run you have to work with, type it in and the depth is just the run divided by the number of treads. Leave it blank and the tool falls back to the old carpenter's rule that twice the riser plus the tread lands near 25 inches for a comfortable stride.
The stringer length is the diagonal of the whole flight — the hypotenuse of the rise and run — so you know how long a board to cut. Two green or red flags tell you at a glance whether the riser and tread fall inside common IRC limits before you start cutting.
Frequently asked questions
Why does a 9-foot rise give 15 steps?
Nine feet is 108 inches. Divided by a target riser of 7 inches that's about 15.4, which rounds to 15 risers. Split 108 back across 15 and each riser is exactly 7.2 inches — right in the comfortable zone and inside code.
What's the difference between risers and treads?
The riser is the vertical face you step up; the tread is the horizontal surface you step on. A flight almost always has one more riser than tread, because the top step lands on the finished floor above instead of another tread.
Is the code check enough to pass inspection?
It flags the common IRC limits — riser no taller than about 7.75 inches and tread at least 10 inches — but local codes differ and there are other rules (headroom, handrails, nosing). Use it as a first sanity check, then confirm with your inspector.