Stair Calculator with 3D Model and DXF Shop Drawings

StairGen Pro checks two things as you type. Comfort: the step formula 2R + G between 600 and 660 mm, a tread depth of at least 280 mm and a pitch between 30° and 40°. And the building code you pick in the Summary panel, with a selector for dwellings or general use: the IRC/IBC (US) by default, or Approved Document K (England), NBC 2020 (Canada), NCC 2022 (Australia) and other national codes. The choice is saved with the project. For each code it checks only the limits that code sets: riser, going between nosings (without the nosing projection), 2R + G, clear width, pitch, risers per flight and guarding height (the model's guarding is 900 mm above the line of nosings, so a code that asks for more, such as the IBC's 42 in, is flagged). Each criterion shows its figure and how far off it is.

• United States · IRC 2021, R311.7 (dwellings): riser height 7¾ in (196 mm) max, tread depth 10 in (254 mm) min, width 36 in (914 mm) min, headroom 6 ft 8 in (2032 mm), handrail at 34–38 in where there are four or more risers, and no more than 3/8 in difference between the largest and smallest riser. Guards on the open side of the stair at least 34 in high (R312.1.2). Commercial buildings follow IBC 1011: risers 4–7 in, treads 11 in min, width 44 in min, and 42 in guards (IBC 1015.3). Source: codes.iccsafe.org. The Summary panel marks these figures as unverified: the ICC site could not be read directly, so they come from official state and county transcriptions.
• United Kingdom · Approved Document K (England), private stair: rise 150–220 mm, going 220–300 mm, 2R + G between 550 and 700 mm, pitch 42° max, headroom 2.0 m (1.9 m at the centre of a loft stair), handrail at 900–1000 mm. Wales, Scotland and Northern Ireland publish their own guidance. Source: gov.uk.
• Australia · NCC 2022, ABCB Housing Provisions Part 11.2: riser 115–190 mm, going 240–355 mm, 2R + G 550–700 mm, 2 to 18 risers per flight and 2.0 m headroom; balustrades are in Part 11.3. Source: ncc.abcb.gov.au.
• Canada · National Building Code 2020, Section 9.8 (stairs within a dwelling): rise 125–200 mm, run 255–355 mm, width 860 mm min and headroom 1950 mm. Provinces adopt their own editions (Ontario, British Columbia, Quebec), so check these figures against your provincial code. Source: NBC 2020, publications.gc.ca.

Code editions change and each state, province or local authority decides which one applies. The check is for guidance only and covers just the limits listed above: it does not check headroom, landings, handrails, the rise of a flight in metres, or the going of spiral treads and winders. Confirm the edition in force with your building department or building control before you build.

The Download DXF button creates a file from your own dimensions, not a generic block from a CAD library. It is saved as AutoCAD 2007 (AC1021), in millimetres or, with the editor switched to inches, in inches with feet-and-inch dimensions, with UTF-8 text, so AutoCAD opens it at the right scale without converting or rescaling anything.

• Dimensioned general arrangement drawing: side elevation, plan and front elevation with heights, lengths and widths.
• One sheet per part (stringer, tread, bracket, landing, post…) with its shop mark, dimensions and quantity.
• One layer per element with ACI colours (STRINGERS, TREADS, BRACKETS, LANDINGS, RAILING, DIMENSIONS, TEXT, MARKS…), so you can switch them off, plot them or send them to the cutting table separately.
• Bill of materials with mark, part, material or section, size, quantity, total length or area and estimated weight.

The marks are the same in the 3D view, the on-screen drawings, the parts list and the DXF: Z1 on the drawing is the Z1 highlighted on the stair.