StairGen Pro › Steel Stair Calculator with Fabrication Drawings
Guide & codes
This steel stair calculator covers the most common job in a fabrication shop: a straight flight on a rectangular tube stringer, single (centre) or double, with a bracket welded under each tread. Enter the total rise (Y), the run available (X) and the stair width (W); the calculator spaces the steps, checks comfort and draws every part for the workshop.
Most metal stair calculators with a diagram stop at rise and run. This one also gives you the stringer, every tread bracket and the railing as separately marked parts, a bill of materials with weights, and steel staircase AutoCAD drawings in DXF built from your own dimensions instead of a generic DWG block. The same model works for steel treads in chequer plate or timber treads on a steel frame: tread thickness (Z) and nosing (F) change the usable tread depth, while the stringer tube (A × G) and the bracket tube (B) change the weight.
When to choose this stair
Choose the straight stair with brackets when the opening is long and narrow and you want the fewest parts: one tube stringer (or two or three, set with T) and an angled bracket under each tread, welded in the shop and installed in one piece. Seen from the side it is the lightest-looking steel stair: the treads seem to float above the stringer.
Compared with the sawtooth version, each tread sits on its own bracket rather than on a tooth, so it can be wider than the structure and a centre stringer stays hidden underneath. The trade-off is one bracket to cut and weld per step. If the opening is too short for a comfortable pitch, don't squeeze the treads: switch to a stair that turns.
Calculator parameters
Each dimension carries the letter used in the editor and on the drawings.
- YTotal rise
- default 2,800 mm · 500 to 8,000 mm
- Height from the lower floor to the finished upper floor.
- XTotal run
- default 4,500 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 16 · 2 to 40
- Steps in the flight, including the top one.
- AStringer depth
- default 100 mm · 30 to 300 mm
- Depth of the stringer tube.
- GStringer width
- default 100 mm · 20 to 300 mm
- Width of the stringer tube.
- BBracket size
- default 100 mm · 20 to 200 mm
- Tube section of the bracket under each tread.
- HHeight over stringer
- default 60 mm · 0 to 400 mm
- Vertical gap between the stringer and the tread.
- DBracket overhang
- default 60 mm · 0 to 300 mm
- How far the tread projects beyond the bracket in the walking direction.
- UBracket angle
- default 10° · -30 to 45°
- Tilt of the bracket from vertical.
- TNumber of stringers
- default 1 · 1 to 3
- One centre stringer, two side stringers or three.
How it's calculated
The total rise Y = 2,800 mm is divided into 16 risers of 175.0 mm. The run X = 4,500 mm is shared between the 16 steps of the flight, giving a run per step of 281 mm; add the nosing F = 50 mm and the tread depth is 331 mm.
The step formula then reads 2 × 175.0 + 281 = 631 mm and the pitch is 31.9°, so the verdict with the default values is “Comfortable stair”. Whenever the formula falls outside 600–660 mm or the pitch goes above 40°, the Summary panel tells you how many steps to add or how much longer X needs to be, and applies the change in one click. For a US dwelling the riser must also stay at or below 7¾ in (196 mm); the code check in the Summary (IRC/IBC by default) flags it when it goes over.
The structure comes from the stringer parameters: the tread sits H = 60 mm above the stringer, projects D = 60 mm past its bracket, and the bracket leans U = 10° from vertical. The bracket spacing along the stringer, listed in the Data tab, is the distance you mark out on the tube before welding. With T = 1 the stair has a single centre stringer (a mono or spine stringer); with 2 or 3, the stringers are spread across the width.
Result with the default values
Comfort verdict: Comfortable stair.
Complies with IRC / IBC
| Step formula 2R + G | 631 mm | 600 – 660 mm |
| Tread depth | 331 mm | ≥ 280 mm |
| Pitch | 31.9° | 30° – 40° |
| Riser | 175 mm | ≤ 197 mm |
| Going | 281 mm | ≥ 254 mm |
| Clear width | 1,000 mm | ≥ 914 mm |
| Guarding height | 900 mm | ≥ 864 mm |
Steps
| Risers | 16 pcs |
| Riser height | 175 mm |
| Run (going) | 281 mm |
| Tread depth (run + nosing) | 331 mm |
| Open riser gap | 125 mm |
| Pitch | 31.9° |
| Nosing-to-nosing distance | 331 mm |
Structure
| Tread area | 5.300 m² |
| Bracket spacing on stringer | 331 mm |
Building codes
The calculator does not size the steel. The tube you choose sets the geometry and the weight, but the strength of the stringers, brackets and welds has to be checked by an engineer under the steel design standard that applies (AISC 360 in the US, Eurocode 3 in the UK, AS 4100 in Australia, CSA S16 in Canada).
Open risers are the norm on steel stairs, and both main codes limit the gap. In US dwellings, the IRC requires that a 4 in (102 mm) sphere cannot pass through an open riser where the stair is more than 30 in above the floor below. Approved Document K asks for treads that overlap by at least 16 mm and openings that stop a 100 mm sphere. The open riser gap shown in the Data tab is the figure to compare.
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- Z1StringerTube 100×100 × 1
- S1BracketTube 100×100 × 1
- S2BracketTube 100×100 × 15
- E1Treadt=50 × 16
- B1HandrailTube Ø42.4 × 1
- B2BalusterRound bar Ø16 × 16
Frequently asked questions
How do you calculate a steel stair?
The same way as any stair: divide the total rise by the number of risers, divide the run by the number of treads and check that 2R + G stays between 600 and 660 mm. Then lay out the stringer, the brackets and the treads. The calculator does both parts at once and adds the bracket spacing, the cut list and the weight.
Is there free steel stair design software that exports DXF?
This calculator runs in the browser, is free and needs no installation or account. It exports a DXF (AutoCAD 2007, in millimetres or inches) with a dimensioned general arrangement, one sheet per part and a bill of materials, ready for the shop or for your architectural drawings.
Single centre stringer or two side stringers?
A centre stringer (T = 1) looks lighter and lets the treads cantilever on both sides, but it works in torsion when someone steps on the edge. Two stringers (T = 2) support the tread near its ends and cope better with wider stairs. Change T and the 3D model, drawings and weight update immediately.
What size tube should I use for the stringer?
The calculator does not choose it for you. The default is a 100 × 100 mm tube, a common size for residential stairs, but the final section depends on the span, the load and the connections, and must be confirmed by a structural calculation.
Can I fit wooden treads on a steel frame?
Yes. Under Finishes you choose the tread material (oak, walnut, chequer plate, laminated glass or microcement) and the bill of materials recalculates the weights with the density of each material.