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Spiral Stair Geometry Calculator Geometric calculator only. Check local building codes.

Total Rise Tread Depth at Ideal Rise Actual Rise Inside Radius Widen Outer Tread Length Draw Chords Rotation ° Draw Stringers

Rotation Inside Radius




Running Measurements explanation
Inside Stringer = tread points winding up and around INSIDE of stairs from top of first rise to upper floor.
Outside Stringer = tread points winding up and around OUTSIDE of stairs from top of first rise to upper floor.
Inside Plumb = tread points vertically (plumb).
Inside Level = tread points around INSIDE LEVEL, (or flat, as marked AROUND a circle on the floor.)

Running Measurements:

Inside Stringer Mark-out

Outside Stringer Mark-out

Inside Plumb Mark-out

Inside Level Mark-out

Left click, release and drag to measure at scale inside diagram.

Spiral stair profile diagram with full dimensions

Spiral Staircase Handrail True Radius Calculator Enter actual rise of handrail for entered angle of rotation.

Flat Radius to Handrail Angle of Rotation Total Height for Rotation