StairGen Pro › Wooden Stair Calculator (Closed Stringers)
Guide & codes
This wooden stair calculator is for the classic joinery stair: two board stringers with the treads housed between them (a closed or housed stringer, “closed string” in the UK) and, if you want, riser boards closing each step. It is the simplest stair to calculate and to build, and the reference for any single straight flight.
From the total rise (Y), the run available (X), the width (W) and the number of steps (C), the calculator gives the riser height, the tread depth and the pitch, checks the step formula and the building code limits (IRC/IBC by default, or Approved Document K, the NBC or the NCC), and produces a cut list of stringers, treads, risers and railing. The diagram is a full drawing set: the stringer sheet in the DXF shows where every housing goes, which is what a woodworking stair calculator with a diagram should give you.
When to choose this stair
Choose the straight wooden stair with board stringers when you want a classic joinery stair, closed at the sides: the treads are housed between two 50 mm stringers that hide their ends and stiffen the flight. It is the easiest wooden stair to make and to fit against a wall or between two partitions.
Compared with the cut-stringer stair, the treads sit between the stringers rather than on top of them, and the side of the stair is a plain board with no visible steps. With riser boards, each step also gets a closed riser, which makes the stair quieter and stops feet slipping through at the back.
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.
- TStringer thickness
- default 50 mm · 20 to 120 mm
- Thickness of the stringer board.
How it's calculated
The total rise Y = 2,600 mm is divided into 15 risers: 173.3 mm per step. The run X = 4,200 mm is shared between the 15 steps, giving a run of 280 mm; with the nosing F = 50 mm the tread depth reaches 330 mm.
Step formula: 2 × 173.3 + 280 = 627 mm. Pitch: 31.8°. Verdict: “Comfortable stair”. If the pitch goes above 40° the stair feels steep even when the step formula works out; the fix is a longer X or, if the opening allows no more, a stair that turns, such as an L-shaped or U-shaped stair with a landing.
The stringers are 50 mm boards and the treads 50 mm. With Riser boards switched on, the closed risers are added as their own parts in the bill of materials; switch them off for an open-riser stair and the open gap appears in the Data tab.
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 |
Wood
| Tread area | 4.455 m² |
Building codes
For a straight flight, the codes mostly limit the rise, the going and the headroom. In the US, the IRC sets a maximum of 7¾ in (196 mm) of rise, a minimum of 10 in (254 mm) of tread and 6 ft 8 in (2032 mm) of headroom measured from the line of the nosings. In England, a private stair may have up to 220 mm of rise and a pitch of no more than 42°. Australia's NCC allows 115–190 mm of rise with a going of 240–355 mm, which is stricter than the UK on the riser.
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- Z1StringerBoard 50 × 2
- E1Treadt=50 × 15
- T1Risert=20 × 15
- B1HandrailRound timber Ø50 × 1
- B2BalusterBatten 35×35 × 15
Frequently asked questions
How do you calculate a straight staircase?
Divide the total rise by a target riser of 170–190 mm (about 7 in) to find the number of risers, round up, and share the run between the treads. Then check that 2R + G stays between 600 and 660 mm. For example, 2600 mm of rise over 14 risers gives 186 mm per step, and the going should then be between 230 and 290 mm.
How much space does a straight staircase need?
In plan, the run X by the width W, plus clear space at the top and bottom. Climbing 2.6 m (about 8 ft 6 in) comfortably takes roughly 3.3 m (11 ft) of run; if you don't have it, an L-shaped or U-shaped stair splits that length into two flights.
What is the 7-11 rule for stairs?
A rule of thumb for a comfortable stair: a riser of about 7 in (178 mm) and a tread of about 11 in (279 mm). Those are the IBC limits for commercial stairs, and they give 2R + G = 635 mm, right in the middle of the comfort range this calculator checks.
Closed stringer or cut stringer?
On a closed stringer the treads are housed between two boards, which hides the end grain and stiffens the stair; it suits interior stairs between walls. On a cut stringer the treads sit on top of notched boards and can overhang at the sides. Both use the same step calculation; the stair stringer calculator covers the cut version.
Open or closed risers?
Closed risers make the stair quieter and stop feet slipping through; open risers are lighter and let light through. Codes limit the gap: 4 in (102 mm) under the IRC and 100 mm under Approved Document K.