Straight stairs

A straight flight of tread and riser boards, laid out to the code it is built for, placed where you want it, and remembered so it can be changed later.

Open it from Shop > Stair calculator... or type /stairs. What it builds is one group called Stairs: a board for every tread, and a board at every riser unless the risers are left open. Stringers are not drawn yet, but the stringer sheet says how to cut them; rails, landings and structure are not built.

Three ways to lay out a flight

1. Typed, then placed

1. With nothing picked, open the stair calculator.
2. Type the total rise (floor to landing), the width, and what it is built for. Suggest works out the number of steps and the run that goes with them.
3. Build stairs. The flight arrives on the cursor, held by the foot of its first riser - click to put it down.

2. Between two lines

1. Draw a level line where the first riser will stand, and another at the landing's edge, at the landing's height. They must be parallel; they need not be the same length or lined up.
2. Pick both lines and open the stair calculator. The rise, run and width come from the lines and cannot be typed.
3. Width from says which line sets the width. The lower line: the flight goes up from it, square, and lands wherever the upper line is. The upper line: it comes down from it, square, to the lower line's distance.
4. The flight is built in place.

3. Picked on the drawing

1. In the dialog, press Pick on the drawing.... The dialog steps aside.
2. Click the top - the landing's edge, at its height. Then the bottom - where the first riser stands. Then the side the width goes, as far out as the stairs are wide.
3. Beside the cursor a small orange flight shows which point the next click is for - 1 TOP, 2 BOTTOM, 3 SIDE - and the points picked carry their names on the drawing. After the top, a dashed line runs to the cursor; after the bottom, the stairs themselves follow the cursor, every step at its height, so the third click is made looking at what it will build.
4. The sizes show as you go: the run and the rise while you look for the bottom; the width, the run, the rise and the steps - how many risers, of what, and the tread - while you look for the side. Instead of clicking, type a length and press Enter, as with any other tool: after the top it is the run, toward the cursor; after the bottom it is the width, on the cursor's side. Arithmetic works here too.
5. Whichever of the two points is lower is the bottom, so clicking them the other way round cannot turn the stairs upside down. Picked level - both on the floor, in plan - the rise is the one typed in the dialog.
6. The dialog comes back with the number of steps that fits your points. Esc at any point goes back to the dialog without picking - and so does picking another tool: the stairs are built or given up on first, so no tool starts with the cursor still picking stairs.

The dialog

Setting	What it is
Total rise	Floor to the top of the landing. Divided evenly among the risers.
Total run	The face of the first riser to the landing's edge. Divided evenly among the treads.
Width	The boards' length across the flight - not the clear width between rails.
Built for	Which rules it is checked against: a house (IRC), public (IBC), older people (gentler), carrying things, accessible (ADA), emergency exit (IBC), service or roof access (OSHA). See the table below.
Risers	How many. The landing is the last step, so 14 risers is 13 treads.
Suggest	Picks the best count for what it is built for. Typed, it sets the run as well. Between lines or picked points it only changes the count - your lines and points stay exactly where you put them.
Board	How thick the tread and riser boards are.
Nosing	How far each tread reaches past the riser below it. It makes the board deeper without changing the rise or the going.
Closed risers	A board at each riser. Off, the risers are open.
Rounded nose	A half-round front edge, radius half the board's thickness.
Open the code it checks against	Opens the official source for the rules chosen.

The side view draws the flight as it stands. Under it, in large type:

• Meets the rules chosen - in green.
• Does not meet them - in red, with each miss on a line of its own: the rise too tall, the tread too short, too narrow. When some other count would fit, it says Suggest finds one.
• Does not fit between your points (or lines) - no number of steps meets the rules in the run you gave it. It says how much run the stairs want and how much more that is than you have: move the bottom out, or turn at a landing.

The box at the bottom holds the notes: the rule in a line, the best fit, the run a target layout wants.

Changing a flight later

The Stairs group remembers how it was made. Right-click it for:

• Change the Stairs... - the dialog on its own values; change anything and it is built again where it stands.
• Print the Stringer Sheet... - the stringer sheet for the flight as it is.
• Build the Stairs Again - puts back anything changed by hand since. Moved since it was made, it is built where it is now.
• Show It in the Source - the line in the drawing's text that says how it was made.

Undo takes the whole flight back in one step. Erasing the group takes only the stairs - a wall or floor face their boards touch stays.

The stringer sheet

Stringer sheet (PDF)... in the dialog, or Print the Stringer Sheet... on a built flight's right-click, writes a few pages to take to the saw, worked out for that flight:

• The numbers - unit rise and run, the step along the pitch, how much the bottom step is cut short (the tread's thickness), and how far the stringers stand back of closed risers.
• What to buy - 2x12 stringers and the board length each needs (and the stock length to buy), how many across the width and how far apart, the throat a cut stringer keeps and whether that is enough, the kicker and the hangers, and the cleats, glue, pins and fasteners for the second way.
• The first way: cut stringers. Get a board at least so long. Every step's outer corner is a dot on the top edge, measured from the squared bottom end; every inside corner is a dot on one chalk line snapped a set distance in. A table gives every dot - along from the end, in from the edge - and the drawing shows the board in rows with the dots numbered, the lines joining them, the waste gray and the cuts dashed red. Connect the dots in order; cut the red lines.
• The second way: solid stringers with cleats. Nothing notched: the same layout, a little lower on the board, marks where a 2x4 cleat goes under every tread and a 1x2 or 2x2 behind every riser - glued, pinned, then nailed or screwed. Only the two ends are cut.

It lays out the cut; it is not an engineered design. Check spans and fastening against the code where the stairs are built.

How the numbers work

Total rise is divided by the number of risers; total run by the number of treads, one fewer. Going is measured between riser faces. Nosing adds to the board's depth, not to the going. The last riser board carries on behind the landing's edge into the landing. Every length box takes typed arithmetic - 8'1" - 3/4" for a floor to be finished later.

Recommendations and reference profiles

The dialog searches whole riser counts against the available rise and run. It reports whether any count fits the selected rise/going/pitch limits, ranks fits near the preferred proportions, and shows the run needed for a target layout. Between lines or points picked, Suggest changes only the count; it never moves your lines or points. If no count fits, the dialog says so even after applying the target count. Building geometry does not certify the design.

Profile	Reference or preference
A house	2021 IRC R311.7: 7 3/4 inch rise at most, 10 inch tread at least, 36 inches wide; with a tread under 11 inches, a 3/4 to 1 1/4 inch nosing.
Retail / public; emergency egress	2024 IBC general stair dimensions: 4–7 inch rise and 11 inch minimum going. Emergency use does not relax these limits. Width, capacity, exceptions and accessible egress need separate evaluation.
ADA stair dimensions	2010 ADA section 504: 4–7 inch rise, 11 inch minimum going, closed risers; nosing projection and edge-radius checks.
Older users	Application comfort preference: target 6 inch rise, 12 inch going; candidate range 4–6.5 inch rise and 12–16 inch going. Width preference 42 inches.
Carrying items	Application comfort preference: target 6 inch rise, 13 inch going; candidate range 4–6.5 inch rise and 12.5–16 inch going. Width preference 48 inches.
Roof / attic workplace service	OSHA standard-stair screening: 30–50 degree pitch, rise no greater than 9.5 inches, going at least 9.5 inches. This is workplace access, not a residential attic-code profile or emergency egress.

Comfort targets and widths are design preferences, not official prescriptions for every older person or load. Rise/going matches do not verify width after handrails, occupant capacity, headroom, landings, load capacity or structural support. The selected lines establish board width, not clear width between rails. Where nosing is used, the landing-edge detail must continue the same projection to maintain uniform nose-to-nose going; the landing itself is not modeled.

OSHA's June 17, 2025 interpretation does not allow extra nosing to compensate for inadequate going. Rounded usable tread surfaces require further checking. Ship stairs and alternating treads are not built by this tool; infrequent access alone does not authorize replacing a standard workplace stair with one.

Official sources

US reference snapshot checked September 28, 2026. Use the edition and amendments adopted for the project. The dialog's reference button opens the relevant official source.

• 2021 IRC, chapter 3 (R311.7 stairways)
• US Access Board: ADA stairways, section 504
• 2024 IBC, chapter 10 (1011.2 and 1011.5.2)
• OSHA 1910.25 stairways
• OSHA: measuring tread depth, June 17, 2025
• HSE manual handling guidance (carrying-use context, not US stair dimensions)

The tool builds tread boards and optional riser boards. Stringers, handrails, turns, headroom checks and structural sizing are not included yet.