StairGen Pro › Steel Stair Calculator with Sawtooth Stringers
Guide & codes
A sawtooth stringer (also called a notched or zig-zag stringer) replaces the straight beam with a stepped profile: each tread rests on a short horizontal length of tube, joined to the next one by an upright. It is the stringer of choice for exposed, architectural steel stairs, and in the shop it is made by cutting and welding short lengths of tube rather than bending plate.
This metal stair stringer calculator spaces the steps from the total rise (Y) and run (X), then breaks each stringer down into horizontals and uprights, each with its mark and quantity. If you prefer a straight stringer with one bracket per tread, use the steel stair calculator instead.
When to choose this stair
Choose the sawtooth stair when you want the steps to show: each stringer is built from horizontal and vertical tube sections in a zigzag, and every tread bears on the full depth of its tooth, with no separate brackets. It is the workshop or loft look, and suits checker-plate or solid timber treads.
Compared with the bracket version it uses two side stringers (T = 2) instead of a centre one, with more cuts and welds, but each tread is supported on both sides. The step layout is the same: with the same height, length and number of steps you get the same riser and the same going, so you can decide on the structure last.
Calculator parameters
Each dimension carries the letter used in the editor and on the drawings.
- YTotal rise
- default 2,600 mm · 500 to 8,000 mm
- Height from the lower floor to the finished upper floor.
- XTotal run
- default 4,200 mm · 500 to 12,000 mm
- Plan length available for the flight (on turning stairs, the upper flight).
- WStair width
- default 1,000 mm · 500 to 2,500 mm
- Clear width of the flight.
- ZTread thickness
- default 50 mm · 3 to 120 mm
- Thickness of the tread (board or plate).
- FNosing
- default 50 mm · 0 to 100 mm
- How far each tread overhangs the one below.
- CNumber of steps
- default 15 · 2 to 40
- Steps in the flight, including the top one.
- AStringer depth
- default 60 mm · 30 to 300 mm
- Depth of the stringer tube.
- GStringer width
- default 40 mm · 20 to 300 mm
- Width of the stringer tube.
- TNumber of stringers
- default 2 · 1 to 3
- One centre stringer, two side stringers or three.
How it's calculated
The total rise Y = 2,600 mm divided into 15 risers gives 173.3 mm per step, and the run X = 4,200 mm over 15 steps gives a run of 280 mm. With the nosing F = 50 mm the tread depth is 330 mm; the step formula is 627 mm and the pitch 31.8°. Verdict: “Comfortable stair”.
On a sawtooth stringer each tooth is one horizontal as long as the going and one upright as tall as the riser, both in 60 × 40 mm tube. That is why rise and run are not just comfort figures here: they are the cutting lengths printed on the sheet of each part in the DXF, so a riser that changes by a few millimetres changes every piece of the stringer.
With T = 2 the stair has two sawtooth side stringers; with T = 1, a single one under the centre of the tread.
Result with the default values
Comfort verdict: Comfortable stair.
Complies with IRC / IBC
| Step formula 2R + G | 627 mm | 600 – 660 mm |
| Tread depth | 330 mm | ≥ 280 mm |
| Pitch | 31.8° | 30° – 40° |
| Riser | 173 mm | ≤ 197 mm |
| Going | 280 mm | ≥ 254 mm |
| Clear width | 1,000 mm | ≥ 914 mm |
| Guarding height | 900 mm | ≥ 864 mm |
Steps
| Risers | 15 pcs |
| Riser height | 173 mm |
| Run (going) | 280 mm |
| Tread depth (run + nosing) | 330 mm |
| Open riser gap | 123 mm |
| Pitch | 31.8° |
| Nosing-to-nosing distance | 329 mm |
Structure
| Tread area | 4.950 m² |
Building codes
The tread and riser rules are those of any straight flight. What is specific to this structure is the welded joint at every tooth: the calculator gives the geometry and the cut lengths, but the tube section and the welds must be checked in the structural design. A channel or plate stringer cut to a sawtooth profile behaves differently from welded tube and is not modelled here.
The calculator checks comfort (2R + G, going and pitch) and the building code of the country you pick in the panel (here, IRC / IBC for a dwelling): only the limits that code sets for riser, going, 2R + G, width, pitch, risers per flight and guarding. It is for guidance only: always confirm the code in force and local rules.
Building codes by country, with sourcesParts with the default values
The DXF (AutoCAD 2007, in millimetres or inches) carries these parts with their shop marks: one dimensioned sheet per part, the general arrangement and the bill of materials with weights.
What's in the DXF- Z1Stringer · horizontalTube 60×40 × 28
- Z2Stringer · uprightTube 60×40 × 2
- Z3Stringer · uprightTube 60×40 × 28
- Z4Stringer · horizontalTube 60×40 × 2
- E1Treadt=50 × 15
- B1HandrailTube Ø42.4 × 1
- B2BalusterRound bar Ø16 × 15
Frequently asked questions
What is a sawtooth stringer?
A stringer shaped like the stair itself, in a zig-zag, with the treads sitting on top of each tooth. In steel it is made from welded horizontal and vertical tube sections; in timber it is cut from a board, and then it is called a cut stringer.
Sawtooth stringer or straight stringer with brackets?
The sawtooth version shows the stepped profile and usually has two side stringers; the straight stringer with brackets is quicker to make because it has fewer cuts and welds. With the same opening, both calculators give the same steps, so you can compare the number of parts and the weight.
Where can I see the length of each stringer section?
In the Drawings tab and in the DXF: every horizontal and every upright has its own sheet with dimensions and quantity. The Parts tab lists them by mark, and hovering over a row highlights the part in the 3D view.