Enter your total floor-to-floor rise and target step size to get riser and tread counts, stringer cut length, a basic materials list, and a check against common code limits.
1. Code Standard
Pick which limits to check your layout against. Local codes vary, so always confirm the exact numbers with your building department.
2. Stair Parameters
Floor to floor
Plumb clearance above the nosing line
Number of Risers / Treads
9 Risers / 8 Treads
Exact Riser Height
7.11 inOK
Tread Depth Entered
10.50 inOK
Total Horizontal Run
84.00 in
Stringer Angle
34.1°
Footprint incl. Nosing
85.00 in
3. Stringer & Materials
A starting materials list. Always round up for waste and confirm against your actual stock on hand.
Stringer Cut Length
101.5 in
Suggested Stock Length
10 ft board
Stringer Boards Needed
3 boards
Tread Stock Needed
8 boards @ 36 in
4. Code & Comfort Check
Riser height vs. IRC maxOK
Tread depth vs. IRC minOK
Headroom vs. code min (80")Enter a value above
Comfort check (Blondel's Rule: 2R + T, ideal 24"-25")24.1 in
How This Is Calculated
Divide your total floor-to-floor rise by your target riser height to get a rough number of steps, then round to the nearest whole number, since you can't have a fraction of a step. Divide the total rise by that whole number again to get the exact, equal riser height every step will use. Treads are always one fewer than risers, since the top "step" is the floor itself. The stringer cut length is just the hypotenuse of the total run and total rise: that's the actual board length you need before notching. Blondel's Rule (2 × riser + tread, ideally 24"–25") is a long-standing rule of thumb stair builders use to check that a stair feels comfortable to walk, separate from what code requires.
Worked Example
For a 9 ft 4 in floor-to-floor rise with a 7.5 inch target riser, this calculator lands on 15 risers and 14 treads, each riser at 7.47 inches, comfortably under the IRC max of 7.75 inches.
Common Mistakes
Forgetting nosing when measuring an existing stair to compare against this calculator's tread depth input, which excludes nosing.
Assuming your local code matches IRC or IBC defaults exactly; many jurisdictions adopt amended versions with different limits.
Not checking headroom clearance, a separate, code-critical measurement this calculator can flag but not calculate from your framing plan alone.
Frequently Asked Questions
What's the difference between IRC and IBC stair code?
IRC covers most residential one and two family homes; IBC applies to commercial and multi-family construction and generally has stricter riser and tread limits.
Why does the calculator sometimes give a riser height different from what I typed in?
It divides your total rise evenly across whole-number steps, so the exact riser height adjusts slightly to keep every step identical, which code requires.
What is Blondel's Rule?
A long-standing comfort formula (2 x riser + tread, ideally 24-25 inches) that stair builders use to check a stair feels natural to walk, separate from code minimums.
Disclaimer: This tool is for planning purposes only. Building codes vary by jurisdiction and project type, and the riser, tread, headroom, and stringer stock requirements shown here are common defaults, not a substitute for your local code or a licensed professional's review. Always verify final dimensions and stringer stock adequacy before cutting.