StairGen Pro › U-Shaped Stair Calculator with Landing
Guide & codes
This U-shaped stair calculator with landing designs a half-turn stair, also called a switchback: two parallel wooden flights joined by a landing that spans the width of both. With the flights side by side and no gap between them, it is what UK builders call a dog-leg stair. It makes the most of a short opening and is the most searched-for of the stairs that turn.
From the total rise (Y), the length of the opening (X), the width of each flight (W) and the steps before (P) and after (Q) the landing, the calculator works out the steps, checks comfort and lists the parts: stringers, landing frame, posts, treads, risers and railing, with the stairwell footprint in the Summary panel.
When to choose this stair
The wooden U-shaped stair with a landing, a half turn with a half landing, is the home stair that fits best into a short opening: the two flights climb side by side and the double-width landing brings you out right above the start. Choose it when you are short of length but have twice the stair width available.
Compared with the 180° winder stair, the landing uses floor area but gives a comfortable turn, without narrow treads next to the newel. A frequent mistake is a landing that ends up too high or too low: with P = 6 and Q = 8 steps you decide where it sits, and the calculator keeps the same riser on both flights.
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 3,250 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.
- PSteps, lower flight
- default 6 · 1 to 25
- Steps before the turn.
- QSteps, upper flight
- default 8 · 2 to 25
- Steps after the turn, up to the top.
- 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 shared between 15 risers: the 6 steps of the first flight, the landing and the 8 of the second. Each step rises 173.3 mm. On the upper flight, X = 3,250 mm minus the landing depth leaves a run of 281 mm and a tread depth of 331 mm.
Step formula: 2 × 173.3 + 281 = 628 mm; pitch: 31.6°; verdict: “Comfortable stair”. On a U-shaped stair the most direct way to bring a high riser down is to add steps to the flights; the Summary panel says how many and in which flight, and a lower riser also makes it easier to meet the 7¾ in (196 mm) IRC limit.
The landing is two stair widths wide (2 × W) and one stair width deep, with a frame of timber beams and two posts. With Reverse turn direction the stair climbs to the left or to the right.
Result with the default values
Comfort verdict: Comfortable stair.
Complies with IRC / IBC
| Step formula 2R + G | 628 mm | 600 – 660 mm |
| Tread depth | 331 mm | ≥ 280 mm |
| Pitch | 31.6° | 30° – 40° |
| Riser | 173 mm | ≤ 197 mm |
| Going | 281 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) | 281 mm |
| Tread depth (run + nosing) | 331 mm |
| Open riser gap | 123 mm |
| Pitch | 31.6° |
| Nosing-to-nosing distance | 330 mm |
Wood
| Tread area | 4.174 m² |
Building codes
At a half landing the stair may not get narrower: the IRC asks for a landing at least as wide as the flight, and Approved Document K for landings at least as wide and as long as the narrowest flight. Because the landing breaks the climb, each flight stays well below the IRC limit of 151 in (3835 mm) of rise per flight and the NCC limit of 18 risers. Check headroom where the upper flight passes under the floor above: 6 ft 8 in (2032 mm) in the US, 2.0 m in the UK and Australia.
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
- Z2StringerBoard 50 × 2
- E1Treadt=50 × 14
- M1Landing frameBeam 50×150 × 2
- M2Landing frameBeam 50×150 × 2
- R1Landingt=50 × 1
- P1PostTimber 100×100 × 2
- T1Risert=20 × 14
- B1HandrailRound timber Ø50 × 1
- B2BalusterBatten 35×35 × 14
- B3HandrailRound timber Ø50 × 1
Frequently asked questions
How do you calculate a U-shaped staircase with a landing?
Subtract the landing depth from the length of the opening, share what is left between the treads and divide the total rise by all the risers, including the one onto the landing. Then check 2R + G. The calculator does it all at once and lets you move steps between the flights.
What are the dimensions of a U-shaped staircase?
Two flights wide and one flight plus the landing long. For a floor-to-floor height of 2.6–3 m (8½–10 ft), a comfortable U-shaped stair usually fits in roughly 2 × 3 m of floor area, depending on the flight width; the Summary panel shows the exact footprint of yours.
Switchback, half-turn and dog-leg: are they the same?
They all turn 180°. Switchback and half-turn are general terms; dog-leg is the UK term for the version with the flights side by side and no well between them, which is how this calculator draws it.
U-shaped stairs with or without a landing?
Without a landing, the turn is made with winders and saves a little floor area: that is the U-shaped winder stair. With a landing it is more comfortable and safer, and you can stop halfway.