Winder Staircase Calculator

A winder staircase uses tapered (pie-shaped) treads instead of a flat landing to turn a corner. A quarter-turn winder uses 3 winder treads to turn 90°, while a half-turn uses 6 winders for 180°. Winders save space compared to landings but must comply with specific Part K rules for the going measurement and minimum tread width. Use our Staircase Calculator for straight staircase dimensions.

It depends on the stair width. Under Approved Document K (Diagram 1.9), for a stair narrower than 1m the going of a tapered tread is measured at the centre of the tread along the curved walk line; for a stair 1m or wider it is measured 270mm in from each side. Crucially, the going of the tapered treads must not be less than the going of the straight flight (para 1.27), and consecutive winders must use the same going (para 1.26). For a private (domestic) stair that going must stay within 220mm–300mm.

Approved Document K (Diagram 1.9) requires a minimum tread width of 50mm at the narrow (inner) end of each winder tread, so it never tapers to a dangerous point. The narrow end runs against the newel post, so the achievable narrow-end width is set by the newel size and the winder angle — a wider newel gives a wider, safer narrow end. In practice many carpenters aim for more than 50mm for surer footing.

A standard quarter turn (90°) commonly uses 3 winder treads at 30° each. You can use 2 winders (45° each) or 4 winders (22.5° each), but the number and the angles must be chosen so the going on the walk line is not less than the straight-flight going (AD K para 1.27). On a narrow stair, fewer winders or unequal angles may be needed to keep the walk-line going at or above the straight going. The winders replace a quarter landing, saving roughly 800–900mm of floor space.

Yes, winder stairs comply with Approved Document K when designed correctly. The key requirements for a private stair are: rise 150–220mm, going 220–300mm, 2R+G between 550mm and 700mm, maximum pitch 42°, a minimum 2000mm clear headroom, a 50mm minimum width at the narrow end, and the walk-line going of every winder no less than the straight-flight going. Building control will check these dimensions.