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

Total Rise Tread Depth at 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 outer tread
Tread Length
Rotation °

Rotation Inside Radius


Spiral stair calculator plan diagram with full dimensions

Spiral stair tread diagram with full dimensions

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

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.

DON'T BREATH THE DUST If you're cutting blocks, concrete, stone or ANYTHING and there's DUST - DON'T TAKE THE RISK
Don't cut it, or cut it wet so there's NO DUST - Silicosis Sucks

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All calculators on this site are geometric only.
Check relevant local regulations for appropriate sizes, spacings and all engineering requirements.

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