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Stair Rise & Run Setout: Riser, Going & the Comfort Formula

How to mark out a stringer by hand — riser height, going, tread count, and the 2R+G comfort check (Blondel's rule) — with a worked example from a real floor-to-floor rise.

The method

Marking out a stringer by hand comes down to three numbers and one comfort check:

  • Riser (R) — how tall each step is. Riser = total rise ÷ number of risers.
  • Going (G) — how deep each step is, nosing to nosing.
  • Treads = risers − 1 — there’s always one fewer tread than riser, because the top and bottom risers land you on a floor, not a tread.
  • 2R + G — the comfort check. Aim for it to land around 600–650 mm, close to a natural stride.

This is independent of any code’s legal minimum/maximum riser and going — it’s the ergonomic maths that sits underneath those limits. Check your local code’s numbers separately; this article is just the setout arithmetic.

Work it out by hand

Say your staircase needs to climb a 2700 mm floor-to-floor rise.

1. Pick a target riser and find the riser count. Aim for something around 180 mm, a comfortable everyday riser height:

2700 ÷ 180 = 15 risers exactly.

If that division isn’t a whole number in your case, round to the nearest whole number of risers, then divide the total rise by that — your riser height will shift a few millimetres from your target, spread evenly across every step, which is exactly what you want.

2. Work out the treads. Always one fewer than the risers:

15 − 1 = 14 treads.

3. Choose a going. Pick 280 mm — a comfortable, common tread depth.

4. Check it against 2R + G.

2(180) + 280 = 360 + 280 = 640 mm

That’s inside the 600–650 mm comfort range — this stair will feel right to climb, not cramped and not a stretch.

So: 15 risers at 180 mm, 14 treads at 280 mm, comfort-checked at 640 mm. That’s everything you need to start marking the stringer.

Do it in 5 seconds

Sources

  • Neufert, Architects’ Data — Blondel’s stair formula (2R + G), the ergonomic basis for the comfort check above.
  • ISO 14122-3, Safety of machinery — Permanent means of access — Stairs, stepladders and guard-rails — general stair geometry principles.

Frequently asked questions

How do I work out riser height for stairs?
Divide the total floor-to-floor rise by the number of risers. A 2700 mm rise split into 15 risers gives exactly 180 mm per step. If the rise doesn't divide evenly, round the riser count to the nearest whole number first, then divide again — you'll land on a riser height a few millimetres either side of your target, spread evenly across every step.
What is the going of a stair?
The going (G) is the tread depth — measured from the front edge (nosing) of one tread to the front edge of the next, not the physical board depth. It's the horizontal distance your foot actually travels per step.
What is the 2R+G rule?
A comfort check, not a legal minimum: two riser heights plus one going should add up to somewhere around 600–650 mm — close to the length of an average adult stride. Land inside that range and the stair feels natural to climb; too far under and it's cramped and steep, too far over and it's a stretch on every step.
How many treads does a staircase have?
Always one fewer than the number of risers. A flight with 15 risers has 14 treads — the first riser lifts you off the lower floor, the last riser lands you on the upper floor, and a tread sits between each pair.
What's a comfortable riser and going for a staircase?
As a starting point, a riser around 170–190 mm with a going around 250–300 mm nearly always lands inside the 2R+G comfort range. A 180 mm riser with a 280 mm going gives 2(180) + 280 = 640 mm — right in the middle. Your local code's legal min/max riser and going limits still apply on top of this — this comfort check is separate from those.