TradesHow this works
Enter the total rise from finished floor to finished floor and the tread depth you want. Code fixes the fewest risers you can use, since each one has to stay under 7.75 inches. The tool lays out that minimum and the next couple of counts, shows the riser height, tread count, and total run for each, and recommends the one closest to a comfortable 7.25 inch riser.
Fewer risers is steeper and fits a tighter space; more risers is gentler but needs more run. Get the total rise right first, because a small error there throws off every step. And confirm the final layout with your building department, since stairs are strict on code.
Common questions
How do I calculate the number of stairs?
Measure the total rise, finished floor to finished floor. Divide by the code maximum riser of 7.75 inches and round up to get the fewest risers you can use. Then divide the rise by that count for the exact riser height. Adding a riser or two makes each step shorter and gentler.
What is the maximum riser height?
The IRC caps residential risers at 7.75 inches, measured nosing to nosing. Every riser in a flight must be equal, within 3/8 inch, because an odd step out of rhythm is a trip hazard. A comfortable riser is closer to 7 or 7.25 inches, which this tool aims for.
What is the minimum tread depth?
The IRC minimum tread depth is 10 inches. Many builders go to 11 inches for comfort, which pairs well with a 7 inch riser. A deeper tread is easier underfoot but adds to the total run, so it needs more floor space at the bottom of the stair.
How much floor space does a staircase need?
The total run is the tread depth times the number of treads, and there is one fewer tread than risers. So a 15 riser stair has 14 treads, and at 10 inches each that is 140 inches, nearly 12 feet of run. If that does not fit, a steeper stair or a landing with a turn may be the answer.
Does this meet code?
It is a planning tool, not a code sign-off. Stairs are a leading injury and inspection point, and riser and tread limits, nosing, headroom, handrails, and landings are all set by your local code. Use this to lay out the stair, then confirm every dimension with your building department before you cut a stringer.
Sources: IRC R311.7.5: max riser 7.75 in, min tread 10 in; risers uniform within 3/8 in (City of Boise/Nampa handouts, Viewrail) · Risers = ceil(rise / 7.75) minimum; total run = tread depth x (risers - 1); comfortable riser ~7 to 7.25 in. Engine version 1.0.0. Risk tier 2.