Spiral Stair Calculator
Calculate spiral staircase dimensions including treads, risers, diameter, height, and angles. Perfect for architects, builders, and DIY home projects.
Step 1: Stair Dimensions
Spiral Stair Standards
Residential: Minimum 60″ diameter, 7.5″ max riser height
Commercial: Minimum 66″ diameter, 7″ max riser height
Tread width: At walking line (12″ from center) should be ≥ 7.5″
Step 2: Design Options
Key Calculations
Riser Height: Total Height ÷ Number of Steps
Tread Depth: π × Diameter ÷ Number of Steps
Total Rotation: 360° × (Steps ÷ Steps per Turn)
Headroom: Critical for code compliance
Spiral Stair Calculation Results
Spiral Stair Dimensions
Spiral Stair Standards Comparison
| Standard | Min Diameter | Max Riser | Min Tread | Headroom | Application |
|---|
Spiral Stair Calculation Formulas
Riser Height Calculation
Formula: Riser = Total Height ÷ Number of Steps
Example: 120″ height ÷ 13 steps = 9.23″ riser height
Tread Depth at Walking Line
Formula: Tread Depth = π × (Diameter – 24″) ÷ Number of Steps
Note: Walking line is 12″ from center, so effective diameter = total diameter – 24″
Example: π × (60 – 24) ÷ 13 = 8.70″
Total Rotation Angle
Formula: Rotation = 360° × (Number of Steps ÷ Steps per Turn)
Example: 13 steps with 13 steps per turn = 360° total rotation
Stairwell Opening Size
Formula: Opening Diameter = Stair Diameter + (2 × 6″) clearance
Minimum: For 60″ stair, opening should be at least 72″ diameter
Example: 60″ stair + 12″ clearance = 72″ minimum opening
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