Spiral Staircase Calculator
Calculate tread dimensions, rise, angle, and all measurements for spiral staircase construction
Calculate Spiral Staircase Dimensions
Basic Staircase Parameters
Center post or open area diameter
Overall staircase width
Floor to floor height
360° = one full turn
Code limit: 9.5 inches
Construction Details
Typical: 34-38 inches
Cost Calculation (Optional)
Spiral Staircase Results
• Tread depth below 7.5" minimum at walking line
• Headroom clearance below 6'6" minimum
• Outside diameter below 5' minimum
Number of Steps: 0.0" ÷ 9.5" = 0 steps
Actual Riser Rise: 0.0" ÷ 0 = 0.00"
Tread Angle: 360° ÷ 0 treads = 0.0°
Tread Length: (0.0" - 0.0") ÷ 2 = 0.00"
Outer Arc: 0.0° × π/180° × 0.0" = 0.00"
Handrail Length: √(0.00² + 0.00²) × 0 = 0.0"
Design Guidelines
Example Calculation
Residential Spiral Staircase
Project: Indoor spiral staircase to second floor
Inside diameter: 12 inches (center post)
Outside diameter: 60 inches (5 feet total width)
Total rise: 9 feet (108 inches floor to floor)
Angle of rotation: 360° (one full turn)
Maximum riser rise: 9.5 inches
Calculation Results
Number of steps = 108" ÷ 9.5" = 11.37 → 12 steps
Actual riser rise = 108" ÷ 12 = 9.0"
Number of treads = 12 - 1 = 11 treads
Tread angle = 360° ÷ 11 = 32.73°
Tread length = (60" - 12") ÷ 2 = 24"
Outer arc = 32.73° × π/180° × 30" = 17.18"
Inner arc = 32.73° × π/180° × 6" = 3.44"
Handrail length = √(17.18² + 9²) × 11 = 233.7" (19.5 ft)
Headroom clearance = 9.0" × 11 = 99" (8.25 ft)
Final result: 12 steps, 11 treads, code compliant design
Building Code Requirements
Staircase Materials
Design Tips
Walking line is typically 12" from inside edge
Consider entry and exit orientation for daily use
Center post provides essential structural support
Add lighting for safety, especially underneath
Include proper handrails and balusters
Template treads before cutting final materials
Understanding Spiral Staircase Construction
What is a Spiral Staircase?
A spiral staircase is a series of steps arranged in a circular pattern around a central axis. Unlike curved stairs that follow an arc, spiral stairs complete at least one full rotation around the center point, creating a compact vertical circulation solution.
Key Components
- •Center Post: Central structural support
- •Treads: Individual step surfaces
- •Handrail: Outer safety railing
- •Balusters: Vertical support spindles
Critical Calculations
1. Number of Steps: Total Rise ÷ Max Riser Rise (rounded up)
2. Actual Riser Rise: Total Rise ÷ Number of Steps
3. Tread Angle: Angle of Rotation ÷ Number of Treads
4. Arc Length: (Angle × π/180°) × Radius
5. Handrail Length: √(Arc² + Rise²) × Number of Treads
Walking Line
The walking line is an imaginary path 12 inches from the narrow end of each tread. This is where tread depth is measured for code compliance (minimum 7.5 inches). The walking line represents the natural path people take when using spiral stairs.