Published 2026-10-29 · 2 min read
How to calculate an indoor staircase: rise, going, width
A wrong staircase is felt in your legs from day one: steps that are too tall tire you, steps that are too shallow make you tread awkwardly. The good news is that a comfortable stair comes from one formula that is three hundred years old.
The formula: two rises plus one going
The French engineer François Blondel noticed that the average human stride is 62–64 cm. A step feels right when twice its rise plus its going (tread depth) gives exactly that: 2R + G = 62–64 cm.
For a house, a comfortable rise is 16–18 cm and a going of 26–30 cm. A 17.5 cm rise with a 28 cm going gives 63 cm — ideal. Local building codes set the legal limits, so check yours, but most fall within these numbers.
A full worked example
Say it is 2.85 m from the ground-floor finish to the upper-floor finish (2.60 m ceiling plus a 25 cm floor slab).
- Divide by the rise you want: 285 / 17.5 = 16.3. Round to 16 risers.
- The actual rise: 285 / 16 = 17.8 cm.
- Going from the formula: 63 − 2 × 17.8 = 27.4 cm. Use 27.5 cm.
- Length in plan: one going fewer than the number of risers, so 15 × 27.5 = 4.13 m.
- Check: 2 × 17.8 + 27.5 = 63.1 cm. Comfortable.
Width and headroom
- Clear width: at least 90 cm for the main stair of a house. Below 80 cm you will not get a wardrobe or a mattress up.
- Headroom, measured vertically from the step nosing: 2.00 m minimum, 2.10 m comfortable. This is where most plans go wrong — the opening in the floor slab ends up too short.
- Handrail at about 90 cm above the nosings, with balusters no more than 10–11 cm apart so a child cannot slip through.
- A landing after at most about 18 risers. A straight 16-riser house stair does not need one.
If you do not have 4 metres
An L- or U-shaped stair splits the run in two. Each turning landing takes a square the width of the stair (for example 90 × 90 cm), but you gain a lot of length. Winders save even more room, as long as at least 10–15 cm of tread remains at the narrow end.
In GrafitGo the Stairs object takes shape (straight, L or U), number of steps, width, total height and total length as parameters. Enter the numbers from your calculation, then walk up at eye level and see whether you hit your head on the slab.
What is the maximum step height?
For main stairs in homes, about 18–19 cm is the usual upper limit, and many codes set it lower. Above 20 cm a stair becomes tiring and risky on the way down.
Does an odd or even number of steps matter?
Not for safety. What matters is that every step has exactly the same rise — a single step one centimetre off is enough to trip you.
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