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The main Navigation tabs at top of each page are Metric - inputs in millimeters (mm)
For Inch versions, directly under the main tab is a smaller 'Inch' tab for the Feet and Inch version.
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Spiral Stair Geometry - Metric
Total Rise
Stair tread codes state that each tread will have a minimum tread depth at specified measurement from narrow edge of tread. CHECK LOCAL CODES (See tread diagram)
Ideal Rise
Actual Rise

Inside Radius
Widen and overlap tread for Newel Post etc - Widened treads must overlap to form correct geometry
Tread Length
Rotation °

Rotation Inside Radius


Spiral stair calculator plan diagram with full dimensions

Spiral stair tread diagram with full dimensions

To print a paper template to mark outside tread curve, go to Full Scale Arc Templates and enter

Running Measurements explanation Not including Tread Widening
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

Outside Stringer

Inside Plumb

Inside Level


Measure at scale 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

Follow Local Building Regulations Be sure to follow local building regulations regarding all stair dimensions.

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Don't cut it, or cut it wet so there's NO DUST - Silicosis Sucks
And if you're cutting wet, wear a mask - theres dust in the spray mist too!

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Check relevant local regulations for appropriate sizes, spacings and all engineering requirements.

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