Basic Spiral Stair Calculator
This tool helps you plan a spiral staircase with accurate measurements. It calculates key details like step height, tread width, travel distance, and headroom clearance — all based on your input.
How This Tool Works
You enter the dimensions of your stair:
- The total rise (height from floor to landing)
- How many degrees you want the staircase to rotate (e.g., 360° for a full turn)
- The outer radius (distance from the centre to the outside edge)
- The number of steps (risers)
Then, choose whether the top platform is standard or flush with the floor. This affects how high each step is.
Once you enter your data and press “Calculate,” the tool shows all results instantly — no wait needed.
Inputs You Can Adjust
- Units: Choose between metric (cm) or imperial (in).
- Switching units changes default values to match standard measurements.
- For example: Metric defaults are 260 cm height, 75 cm radius; Imperial is 102 in height, 30 in radius.
- Stair Height: Total rise from floor to landing (e.g., 260 cm or 102 in).
- The tool automatically suggests a number of steps based on typical riser size (~18.5 cm or ~7.25 inches).
- Rotation: How many degrees the staircase makes — e.g., 360° for one full turn, 180° for half.
- Radius (Outer): Distance from centre to outside edge of step (e.g., 75 cm or 30 in).
- This affects tread width and travel distance.
- Number of Steps: How many risers you want.
- If you change this, the tool recalculates height per step accordingly.
- Mount Option: Choose between:
- Standard Mount — top platform is one step below floor level.
- Flush Mount — top platform sits level with floor (so each step becomes taller).
What This Calculator Shows
After you input your values, it gives you:
- Number of Risers: How many steps you’ll have.
- Riser Height: How high each step will be in cm or inches.
- Angle per Step: How much the staircase turns per step (e.g., 360° / number of steps).
- Outer Tread Width (Arc): The length of the outer edge of each step — this is based on radius and angle.
- Total Travel Distance: How far you walk along the outside path.
- Required Well Opening: Diameter needed for a safe clear space in the centre.
- Headroom Clearance: Whether there’s enough vertical clearance above the staircase (e.g., 200 cm or 78 inches — minimum).
If headroom is “OK”, it means you have sufficient clearance
If headroom is too low, your ceiling may be too short for safety.
Why This Matters
Spiral stairs are great space-savers but can be dangerous if not designed properly.
This tool checks that:
- The riser height is safe and comfortable (not too high or too low).
- The tread width is usable.
- There’s enough headroom — especially important in tight spaces.
It also helps you avoid the common mistake of making steps too narrow or too high, which can lead to falls.
Tips for Best Results
- Use a standard mount if you have limited floor height (e.g., 2.4m).
- For flush mount, ensure your ceiling is at least 2.6m tall.
- Always check that the final headroom meets local building code requirements (usually at least 200 cm or 78 inches).
How to Use This Tool
- Enter your measurements in either metric or imperial units.
- Set rotation to 360° if you want a full turn; use 180° for half-turns.
- Choose the mount option based on where your landing is located.
- Watch the results update automatically as you type.
You don’t need to click “Calculate” — every input change triggers an instant calculation.
What’s Included in the Diagram
The diagram shows a simplified view of a spiral staircase:
- A central hole (well opening)
- Outer radius
- one step
Final Thoughts
This tool makes planning spiral stairs easier. Whether you’re building a garden or an attic stair, it ensures safety and usability.
Use it to double-check your design before construction begins.
Always confirm with local codes and consider professional advice if unsure.
Note: This calculator is meant for informational use only — not official architectural guidance.