L‑Shaped & U‑Shaped Staircase Calculator
Design quarter‑turn (L), half‑turn (U) and winder stairs — Stairs Calc sizes each flight, lays out the turn, and checks winder treads at the walkline.
Two flights with a 90° landing between them (quarter-turn).
Finished floor to finished floor — split across the flights.
The depth you step on, not counting the nosing.
Top of the rail above the nosing line. Applied to every flight.
How the handrail turns at the landing — square corners (straight) or a smooth wreath (curved). Shows in the 3D model.
The turn landing — at least as deep as the stair is wide.
Move the landing up or down the flight — the plan and 3D model follow. The landing doesn't have to sit in the middle.
Flight 1
Steps (risers)
16
15 treads
Riser height
7"
177 mm
This flight's rise
9' 3 3/4"
2.839 m
Tread run
11"
279 mm
Total run
13' 8 3/4"
4.185 m
Stringer length
16' 7 1/16"
5.057 m
Flight 2
Steps (risers)
15
14 treads
Riser height
7"
177 mm
This flight's rise
8' 8 3/4"
2.661 m
Tread run
11"
279 mm
Total run
12' 9 3/4"
3.906 m
Stringer length
15' 6 1/16"
4.726 m
Landing & footprint
Landing depth
3'
914 mm
Turn
90°
quarter-turn
Footprint length
16' 8 3/4"
5.099 m
Footprint width
15' 9 3/4"
4.82 m
Winder tread rules
Winders are the pie-shaped treads that carry a stair around a turn instead of a flat landing. The IRC measures their depth at the walkline, an arc 12″ in from the inside of the turn, and requires:
- at least 10″ of tread depth at the walkline (matching a straight tread),
- never less than 6″ anywhere across the tread, and
- the same equal-riser rule as the rest of the flight (IRC R311.7.5.2.1).
Size the straight flights with the calculator above, then place the turn so the winder treads keep their walkline depth.
L vs U vs winder
- L-shaped (quarter-turn) — one 90° turn, usually with a landing; fits a corner and adds a natural rest point.
- U-shaped (half-turn) — two 90° turns with a landing between, doubling back so the stair occupies the smallest floor footprint.
- Winders — replace the landing with pie treads to save even more space, at the cost of a trickier, steeper-feeling turn. For the tightest footprint of all, compare a spiral staircase calculator.
If you’d rather keep a flat landing at the turn, the stairs-with-landing calculator sizes each flight and checks the landing.
Frequently asked questions
How do you calculate L‑shaped stairs?
Split the total rise into the flights on either side of the turn, size each run the same way as a straight stair, then lay out the landing or winders at the 90° corner. Stairs Calc sizes each flight and lays out the turn for you.
What are winder stairs and are they to code?
Winder stairs are wedge‑shaped treads that turn the staircase without a flat landing. Under IRC R311.7.5.2.1 they are allowed if the tread is at least 10″ at the walkline and never less than 6″ at any point.
How much space does a U‑shaped staircase need?
A U‑shaped (half‑turn) staircase stacks two parallel flights with a landing between, so its footprint is roughly twice the stair width plus the landing — more compact in length than a straight run but wider. Stairs Calc shows the footprint in the 3D model.
Where is the walkline measured?
The walkline is the path 12″ in from the inside edge of the turn; winder tread depth is measured along it. Stairs Calc sizes winder treads at the walkline so they meet the 10″ minimum.
Related stair calculators
Written by the Stairs Calc editorial team. Methodology and code references: see our methodology.
Built and maintained by builders, drafters and engineers who plan stairs for a living — every code limit is transcribed from the published standard and cited to its exact section.
Last reviewed 2026-06-20 against IRC 2021/2024
Stairs Calc gives accurate geometry and checks it against published building-code limits, but results are estimates for planning. Codes are adopted and amended locally and change over time. Always confirm dimensions against your local adopted code and a licensed professional before you build.