Winder Staircase Calculator — Tapered Tread Rules & Walking Line

Winders — the tapered treads that turn a staircase through a corner — have their own geometry rules in Approved Document K: the going is measured on the walking line (the centre of the flight for stairs under 1m wide, 270mm from each side for wider flights), it must meet the same minimum as the straight treads, and the narrow end must never be less than 50mm. This calculator takes your stair width and the number of winders in the 90° turn, and tells you whether the geometry passes — before the joinery drawing is even started. The single most common question after a failed straight-flight check: "will winders fix it?" — this tool answers it.

220mm
Min Going @ Walking Line
50mm
Min at the Narrow End
270mm
Measure Point (Flights ≥1m)
3
Classic Kite Winder Set
Free Geometry Tool

Winder Calculator

Stair width + winders in the turn — going on the walking line, narrow-end check, verdict.

900mm
200mm
Winder Geometry Result
PASS ✓
This winder set complies with Approved Document K for a private staircase
236mm
Going @ Walking Line
52mm
Narrow End
636
2R+G @ Walking Line
900mm²
Corner Footprint
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Indicative check for a 90° quarter-turn with equal-angle winders on a private staircase (England & Wales). The walking line is taken at the flight centre for widths under 1m and at 270mm from each side for wider flights, per Approved Document K. Consecutive tapered treads must use a uniform going on the walking line, and the winder going must not be less than the going of the straight treads. Final setting-out is confirmed at survey.
Quick Answer — At a Glance

Winder treads are legal in the UK when three conditions hold: the going measured on the walking line — the centre of the flight for stairs narrower than 1m, or 270mm from each side for wider flights — meets the same minimum as the rest of the stair (220mm private); the narrow end is at least 50mm; and the rise stays identical to the straight treads. The classic solution is three kite winders turning 90° within a square roughly equal to the stair width — at 900mm wide with a standard newel, the walking-line going comes out around 235mm, which passes. Four winders in the same 90° usually fails (going drops below 220mm), and widening the stair past 1m moves the measurement point to 270mm from the inside, which makes winders dramatically harder to pass — the counterintuitive rule this calculator exists to catch.

How Winder Going Is Measured

going per winder = (90° arc at walking-line radius) ÷ number of winderswalking line: centre of flight (width < 1m) · 270mm from each side (width ≥ 1m) — AD K

On a straight tread the going is the same everywhere; on a winder it varies from almost nothing at the newel to generous at the outside. The regulations resolve this by defining where you measure: along the line people actually walk. For a 900mm-wide flight, that's 450mm from the inside — three winders give a going of about 235mm there, and the flight feels consistent underfoot because the walking-line 2R+G matches the straight treads. Push to four winders and each one's share of the 90° arc shrinks below the minimum; the stair becomes a hazard exactly where people pivot.

WINDER GEOMETRY — PLAN VIEW 3 kite winders through 90° — going measured on the walking line newel WALKING LINE going ≥ 220mm measured here, each winder equal narrow end ≥ 50mm no tread may taper below 50mm corner footprint ≈ stair width × stair width WIDTH < 1m walking line = centre of the flight WIDTH ≥ 1m measure 270mm from each side — winders get much harder to pass Same rise as the straight treads · uniform winder going · 2R+G on the walking line The three conditions every compliant winder set satisfies — Approved Document K

Three kite winders through 90°: the going is checked on the walking line, the taper is checked at the narrow end.

The 1-metre trapWidening a staircase normally makes everything easier — with winders it's the opposite. The moment the flight reaches 1m wide, the going is no longer measured at the generous centre but at 270mm from the inside, where the winders are at their tightest. A three-winder set that sails through at 900mm wide fails badly at 1,000mm. The fixes: keep the flight under 1m through the turn, spread the turn over more space with a larger newel radius, or swap the winders for a quarter landing — which needs more footprint but has no tapered-tread rules at all. Check the straight sections either side with the rise & going calculator.

Winders vs Quarter Landing — The Trade

Winders win on footprint: three risers climb inside the corner square, so the staircase gains ~700mm of height in space a landing would spend flat. Landings win on safety and simplicity: no tapered treads, easier to carry furniture around, friendlier for children and older users, and no walking-line mathematics for Building Control to query. On cost they're close — winders need more complex stringers and treads; a landing needs its own structure. Our rule of thumb from installations: if the straight-flight check fails by less than ~700mm of run, winders solve it elegantly; if it fails by more, the layout wants a landing (or a rethink of the stair position — see the loft checker for the tightest cases).

Uniformity applies to winders too. All winders in a turn must have the same going on the walking line as each other — and it must not be less than the going of the straight treads. A "2+1" arrangement with unequal angles, or winders meaner than the straight flight, breaks the rhythm at exactly the point where people are turning and can't see their feet. It's the detail Building Control measures with a tape on inspection day, and the reason winder staircases are set out with CAD, not on site.

Winders — FAQ

Common questions about tapered treads and quarter-turn staircases.

Yes — tapered treads are fully permitted under Approved Document K, provided: the going measured on the walking line (flight centre under 1m wide; 270mm from each side at 1m or wider) meets the same minimum as the straight treads; the narrow end is at least 50mm; the rise is identical to the rest of the flight; and consecutive winders have a uniform going.
In practice three — the classic kite winder set at 30° each. Two winders (45° each) pass comfortably but climb one riser less. Four winders squeeze each tread's share of the arc so far that the walking-line going usually drops below 220mm on domestic widths — the calculator above shows exactly where the line falls for your width and newel detail.
On the walking line: for flights narrower than 1m, the centre of the flight; for flights 1m wide or more, 270mm from each side — and the going must comply at that measurement point. This is why wide staircases with winders are counterintuitively harder to make compliant than narrow ones.
Compliant winders are safe for everyday use — the walking-line rules exist precisely to keep the stride consistent through the turn. They are statistically less forgiving than straight flights or landings for very young children, older users and furniture moves, which is why a continuous handrail through the turn is strongly recommended (and required where the flight needs one), and why a quarter landing is the better choice where footprint allows.
They're comparable. Winders add fabrication complexity — tapered treads, curved or mitred stringers, CAD setting-out — typically £400–£900 over an equivalent straight section on a bespoke staircase. A quarter landing adds its own structure and consumes ~1m² of floor. The decision is almost always driven by footprint, not price — winders buy three risers of climb inside the corner square.
Winder Staircases by Continox

Set Out in CAD, Right First Time

Every Continox winder staircase is set out in CAD with the walking-line geometry checked before fabrication — steel, oak and glass, compliant through the turn. Free site survey, 3D visuals, fixed price within 24 hours.

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