Calculator inputs
Enter your project dimensions in millimetres, then calculate the stair geometry and material area.
Example data table
| Item | Example value |
|---|---|
| Floor-to-floor height | 3000 mm |
| Outer diameter | 1800 mm |
| Center column diameter | 250 mm |
| Total turns | 1.50 |
| Desired riser | 175 mm |
| Exact riser result | 176.47 mm |
| Walking line going | 352.87 mm |
| Pitch angle | 26.57° |
Formula used
1. Number of risers
Steps = round(Total Height ÷ Desired Riser)
2. Exact riser height
Exact Riser = Total Height ÷ Steps
3. Usable stair width
Width = (Outer Diameter ÷ 2) − (Column Diameter ÷ 2)
4. Total rotation
Total Angle = Turns × 360°
5. Angle per step
Angle per Step = Total Angle ÷ Steps
6. Walking line going
Going = 2π × Walking Radius × (Angle per Step ÷ 360)
7. Pitch angle
Pitch = arctan(Exact Riser ÷ Walking Line Going)
8. Approximate headroom
Headroom ≈ Rise per Full Turn − Tread Thickness
How to use this calculator
- Measure the finished floor-to-floor height.
- Enter the outer diameter and center column diameter.
- Choose your desired riser, total turns, and tread thickness.
- Set the required headroom and walking line position.
- Add a waste percentage for material planning.
- Press Calculate Staircase to display results above the form.
- Review the checks, graph, and downloadable summary before finalizing drawings.
FAQs
1. What does this spiral staircase calculator estimate?
It estimates riser count, exact riser height, tread travel at several radii, pitch angle, approximate headroom, helical walking length, and total tread area. It helps with layout planning before detailed engineering or shop drawings.
2. Why is the walking line important?
The inner edge is too tight and the outer edge is too generous. The walking line gives a more realistic travel path, so going and pitch calculations better reflect how people actually use a spiral stair.
3. How are the number of steps chosen?
The calculator divides total height by your target riser, then rounds to a practical whole number. It recalculates the exact riser so the full vertical height is met evenly across the staircase.
4. Does this replace code review?
No. Stair codes vary by country, occupancy, and application. Always confirm minimum width, allowable riser, required headroom, guard requirements, landing geometry, and structural rules with the authority having jurisdiction.
5. What does approximate headroom mean here?
It estimates clearance by comparing the rise gained in one full turn with tread thickness. That is useful for early planning, but actual headroom also depends on openings, landings, slab edges, and finish layers.
6. Why can a stair feel steep even with a fair riser?
A spiral stair can still feel steep when the walking line going is short. Comfort depends on the riser and the horizontal travel working together, not on riser height alone.
7. What material estimate is included?
The calculator estimates plan-area tread material from annular sector geometry and adds an optional waste allowance. It does not estimate stringers, center column steel, balusters, rails, fixings, or finish losses.
8. Can I use this for metal, wood, or concrete stairs?
Yes, for conceptual geometry. The layout math works across common materials, but structural capacity, fabrication limits, connection design, tread thickness, vibration, and finish build-up still need project-specific engineering.