Winder Stair Calculator

Calculate riser height and walk-line tread depth for 90-degree winder turns.

Total Floor-to-Floor Rise (mm)

Desired Riser Height (mm)

Stair Width (mm)

Number of Winder Treads 2 Treads (45° each) 3 Treads (30° each) 4 Treads (22.5° each)

Walk Line Offset (mm)

Inner Corner Radius (mm)

Calculation Results

Total Number of Risers
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Actual Riser Height
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Winder Tread Angle
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Tread Depth at Walk-Line
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Understanding Winder Stair Design

Winder stairs are a space-efficient alternative to stairs with a standard landing. Instead of a flat platform to turn 90 or 180 degrees, "winders" use wedge-shaped treads to change direction while continuing the vertical climb. This is particularly useful in tight architectural layouts or renovations where space is at a premium.

Key Components of a Winder Turn

Total Rise: The vertical distance from the top of the finished lower floor to the top of the finished upper floor.
The Walk Line: This is the path most people take when walking up or down the stairs. It is typically measured 12 inches (300mm) from the inner edge (the narrow side).
Tread Depth at Walk-Line: For safety and compliance, the width of the tread at the walk-line should be consistent with the straight treads in the staircase.
Inner Corner Radius: The radius of the curve on the inside stringer. A larger radius allows for a wider "point" on the winder, increasing safety.

Safety and Building Codes

Most building codes (such as the IRC in the US or Approved Document K in the UK) have strict requirements for winders to prevent trip hazards:

Minimum Tread at Narrow Side: Usually, the narrowest part of the winder tread must be at least 6 inches (152mm).
Walk-Line Consistency: The depth of the winder tread at the walk-line must match the depth of the straight treads within a specific tolerance.
Riser Uniformity: All risers in the entire flight must be equal to avoid breaking the user's rhythm.

Example Calculation

If you have a Total Rise of 2600mm and a Target Riser of 180mm:

Total Risers = 2600 / 180 = 14.44 (Round to 14 or 15).
If choosing 15 risers: Actual Riser Height = 2600 / 15 = 173.33mm.
For a 3-tread winder turn (90° total), each tread angle is 30°.
If the Walk Line is 300mm from the inner edge and the inner radius is 50mm, the radius at the walk line is 350mm.
Walk-Line Tread Depth = (30° / 360°) * 2 * π * 350mm ≈ 183.26mm.