Stair Calculator
Solve risers and treads to IRC limits — max 7¾" riser, min 10" tread.
Estimates only — verify with local code and the product label.
How this works
Residential stairs in Minnesota follow the IRC (Minnesota Rule 1309 adopts the IRC with state amendments), which sets hard limits rather than suggestions: no riser taller than 7¾" (IRC R311.7.5.1), and no tread run shorter than 10" (IRC R311.7.5.2). This tool solves for the fewest equal risers that keep every riser at or under that 7¾" maximum, given your total rise from the lower surface to the upper one.
The math is straightforward once you see it: risers = the total rise divided by 7.75", rounded up to a whole number, then that whole rise is split evenly across that many risers so each one comes out equal (uneven risers are both against code and a genuine trip hazard). Tread count is one less than riser count, because the top of the flight is the deck or floor surface itself — it isn't a separate tread.
The tool also flags two more requirements that trip people up: a handrail is required once a flight has 4 or more risers (IRC R311.7.8), and a guard (the railing along an open side) is required once the walking surface is more than 30" above grade or the floor below within 36" horizontally (IRC R312.1.1). Both show up automatically based on your inputs.
This solves a straight flight only — it doesn't handle winders, landings mid-flight, or spiral stairs, and it doesn't replace a local building official's review of your actual plan.
Frequently asked
Why is my tread count one less than my riser count?
Because the top step of most stairs is the deck, porch, or floor you're stepping onto — that surface does the job of the last tread, so it isn't built or counted separately.
What if my tread run is under 10"?
The tool will flag it — 10" is the IRC minimum (R311.7.5.2). A shorter run also usually requires nosing between 3/4" and 1 1/4" (R311.7.5.3) to keep the effective tread depth adequate.
Questions about a project? Contact us.