Stair calculator
Floor-to-floor height in, a buildable flight out: equal risers, a going that matches your stride, the pitch, and how much floor the stair actually takes.
Opens the editor with the flight already placed — 17 steps over its 4.48 m run. Stairs are parametric, so change the count or switch to an L or U and the treads relay themselves.
The formula
risers = round(rise ÷ target riser), then riser = rise ÷ risers —
every step identical. For the defaults: 3000 ÷ 175 ≈ 17.1, so
17 risers of 3000 ÷ 17 = 176.5 mm.
With a 280 mm going that scores 2 × 176.5 + 280 = 633 mm on the
2R + G stride rule (aim for 600–650), at a pitch
of 32.2°. A straight flight has one fewer tread than risers — the top "tread" is the
upper floor itself — so it runs 16 × 280 = 4.48 m in plan.
These are comfort conventions, not building code — codes set national hard limits on top (riser, going, pitch, headroom, width). The checks in the form mark the comfortable zone.
Common questions
Related: room sizes & clearances for stair widths and landings, the glossary for riser/going vocabulary, and adding a storey for where the floor-to-floor height comes from.
What is a comfortable riser height and going?
The rule of thumb used across most of Europe is 2R + G between 600 and 650 mm — twice the riser plus the going should match a natural stride. In practice that means risers of 150–190 mm with goings of 250–320 mm; the classic comfortable pair is around 175/280. Steeper than 190 mm feels like a ladder; shallower than 150 mm trips people who expect a taller step.
Why does the calculator round to a whole number of risers?
Every riser in a flight must be identical — a single odd step is the classic trip hazard, and most codes forbid a variation of more than a few millimetres. So the floor-to-floor height is divided into a whole number of equal risers, and the riser you get is that division, not the target you asked for. The Gridsnap editor works the same way: its parametric stairs divide the storey height into equal risers automatically.
Is this a building-code check?
No — these are comfort conventions, not regulations. National codes set hard limits (a common pattern for private stairs: riser at most 190–220 mm, going at least 220–250 mm, pitch at most 42°, headroom at least 2000 mm) and they differ by country and by whether the stair is a main or a secondary one. Check your jurisdiction before building; use this to land in the comfortable zone first.
How long does the stairwell opening need to be?
Long enough that your head clears the floor above — about 2000 mm of headroom measured vertically above every tread nosing. Count how many risers you descend before your head passes under the floor edge: roughly (floor thickness + 2000) ÷ riser. The opening must span the remaining treads. The honest answer is that this is exactly the kind of geometry worth drawing rather than computing: put the stair on a plan with the floor above and the section answers it.
What about landings and turning stairs?
A landing takes the place of one going in plan but no riser — the flight keeps climbing after it. An L (quarter-turn) or U (half-turn) stair has the same riser arithmetic as a straight one; only the plan footprint folds. In Gridsnap, straight, L and U stairs are all parametric: set width, the space you have, and the number of steps, and the treads and landing are laid out for you.
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See the stair in the building, not in a table
Draw the flight on the plan and Gridsnap shows it in 3D and section context — including whether it actually fits the hall.