Spiral Stair Calculator
Calculate spiral staircase dimensions including diameter, rotation degrees, rise per step, and building code compliance.
How It Works
Enter the total rise, desired diameter, and center column diameter. The calculator determines the number of steps, rise per step, rotation per step (degrees), total rotation, tread dimensions at the walk line (12" from the narrow end per IRC code), and whether the design meets building code requirements. Spiral stairs have special code provisions: minimum 26" clear width, minimum 7.5" tread depth at the walk line, and a center column for structural support.
Frequently Asked Questions
What are the code requirements for spiral stairs?
IRC 2018 spiral stair requirements: minimum 26" clear width (measured from center column to outer edge), minimum 7.5" tread depth at the 12" walk line, maximum 9.5" riser height, minimum 6'6" headroom, and the stairway must have a handrail.
What diameter do I need for a spiral staircase?
Minimum code-compliant diameter is 60" (5 feet) for a spiral stair serving as a required means of egress. For comfort, 66-72" is recommended. For secondary/decorative spiral stairs, smaller diameters may be acceptable per local code.
How many degrees of rotation per step?
Typical rotation is 22.5° to 30° per step, with a full 360° rotation taking 12-16 steps. The rotation depends on the number of steps and total rise. More steps with less rotation per step is generally more comfortable.