Staircase Calculator
Design your staircase and see a to-scale side-view diagram that reveals if the steps are actually comfortable — before you cut a single board.
in centimeters
in centimeters
in centimeters
for headroom collision check
in centimeters
Why Most Staircase Calculators Get It Wrong
Standard staircase calculators give you a number of steps and call it done. But two staircases with identical step counts can feel completely different to walk on — one comfortable, one exhausting or even dangerous. The missing piece is ergonomics: how an actual human body moves through the space.
This calculator uses the Blondel formula, a 17th-century French architectural principle still used today, which states that twice the riser height plus the tread depth should fall between 60 and 65 centimeters. This range corresponds to the natural stride length of an average adult walking on a flat surface, adjusted for the vertical effort of climbing.
How the Comfort Index Works
The Comfort Index scores your staircase from 0 to 100 based on three factors: how close the riser height sits to the ideal 17.5cm, how close the tread depth sits to the ideal 28cm, and whether the resulting angle falls within the comfortable 30-35 degree range. A score above 85 indicates a professionally comfortable stair. Below 45 suggests the design needs rethinking before construction begins.
Example Calculation
Scenario: Total rise 280cm, total run 350cm, width 90cm, straight staircase.
- Number of steps: 16
- Riser height: 17.5cm
- Tread depth: 28cm
- Angle: 32°
- Comfort Index: 94/100 — Excellent
The Headroom Mistake Nobody Warns You About
One of the most common and costly errors in DIY staircase construction is insufficient headroom — the vertical clearance between a tread and the ceiling or floor opening directly above it. A person climbing the stair can strike their head on a floor joist or opening edge that looked perfectly fine on a flat 2D drawing. Most building codes require at least 200cm of clearance measured vertically from the surface of each tread, and this calculator flags designs that fall short of that threshold.
Why the Comfort Index Matters More Than Raw Numbers
A riser height of 19cm and a tread depth of 24cm might look acceptable on paper, satisfying minimum building code requirements in many jurisdictions. But climbing it repeatedly reveals a different story: the steep angle forces an exaggerated knee lift on every single step, which becomes genuinely tiring on a daily basis and risky for children, elderly residents, or anyone carrying items up and down. The Comfort Index models approximate human leg proportions to surface this kind of problem before construction, not after.