Stair Ergonomics Explained

Why riser and tread proportion matters, how the ergonomic formula works and quick checks you can trust during design.

Core idea – what makes a stair feel natural?

Comfort on stairs is about rhythm. People walk with a natural stride: stairs that match that stride feel effortless. The practical rule widely used by architects and builders is: 

2 × rise + run ≈ 600-640 mm

Here "rise" is the vertical height of one step and "run" (sometimes called "going" or "tread") is the usable horizontal depth. If your design stays close to this relation, users can climb and descend with a natural step length.

Target ranges and quick checks

  • Practical riser range: 120-200 mm. For indoor comfort target 150-180 mm.
  • Tread depth (run): commonly 230-300 mm. For comfortable stride prefer 250-280 mm.
  • Angle: comfortable 30-37°; >42° usually too steep.
  • Consistency: keep risers and runs uniform across the flight (tolerance ≤ 5-10 mm).

Tip - when in doubt use the Stair Calculator and check multiple step counts. Small changes in step count often bring the design back into the ergonomic band.

Why the 2 × rise + run rule works

The formula approximates a human stride by combining vertical and horizontal elements of a step. It is not law but a reliable heuristic:

  • If 2 × rise + run is much less than 600 mm the stair feels short and quick (many small steps).
  • If it is much more than 640 mm people must take long steps, which feels tiring or unstable.

Use the formula alongside riser/run hard limits (120-200 mm and 230+ mm respectively) and angle checks to form a robust rule set.

Design workflow – practical checklist

  1. Measure total rise (floor-to-floor). Estimate available run or set a desired tread depth.
  2. Try step counts near rise / 170 mm (approx). Use the calculator to preview options.
  3. Check each candidate against the 2 × rise + run rule and the riser/run ranges.
  4. Ensure headroom and handrail conditions meet local code.

Examples

Example A: total rise 2800 mm. 15 steps → rise ≈ 186.7 mm. With run ≈ 250 mm → 2×186.7 + 250 ≈ 623.4 mm → Good.

Example B: total rise 2000 mm. 10 steps → rise 200 mm. If run ≈ 230 mm → 2×200 + 230 = 630 mm → technically acceptable but riser at top limit - check comfort.

When angle matters more than the formula

For very shallow or very steep flights the angle check can override the formula. Example: if rise/run gives an angle >42° the flight is too steep regardless of formula. Conversely, very shallow angles (<30°) may be comfortable but require a long run.

Tools and quick links

Try the Stair Calculator and the Slope to Degree Converter to test real cases.