Comfort
Using the Blondel Formula for Comfortable Stairs
Learn what the Blondel formula means and how to use it to balance riser height and tread depth.
What the Formula Measures
The Blondel rule compares two riser heights plus one going. In metric design this target is often near 600 to 640 mm, depending on local practice and the intended use.
The point is not to chase a magic number. It is to keep the walking rhythm close to a natural stride.
Why It Helps
A stair can fit in plan but still feel awkward. The Blondel value catches many of those awkward combinations before they become expensive construction details.
If the result is too low, the stair often feels flat and long. If it is too high, it can feel steep or tiring.
Use It With Constraints
Always combine the Blondel check with local code, headroom, landing dimensions, and the real available opening.
For renovation work, compare several layouts before committing to a final stairwell cut or stringer design.
Put this into practice now
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