Spiral stair calculator
Estimate spiral tread rise, rotation, and walking-line run from explicit turn and center-column topology.
What you enter
- Total rise (in)
- Maximum riser (in)
- Stair diameter (in)
- Local minimum (in)
- Total turns (rev)
- Center column diameter (in)
- Walking radius (optional) (in)
Main results
- Number of risers
- Number of treads
- Total rotation (deg)
- Angle per tread (deg)
- Walking-line radius
- Walking-line run
- Tread run at the walking line
- Review status of the minimum you typed
What it follows
Plain geometry on the turn and center-column numbers you type; no building-code table is looked up. The local minimum diameter is a number you type; it is recorded with the result and marked for review.
Every result is marked REVIEW REQUIRED. Illustrative project-planning values only; jurisdiction, species, grade, loads, wet service and current adopted tables require review. Do not use a result directly for permit, purchase, or field use.
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The calculator opens inside the designer, after you sign in.
Accounts are issued by the DeckAndShed team. There is no self-service sign-up.