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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

Riser = total rise ÷ number of risers. Treads = risers − 1. The going (G) is the tread depth, nosing to nosing. Then run the comfort check: 2R + G should land around 600–650 mm. That is close to a natural stride.

This check is not the law. Your local code sets legal riser and going limits as well. Check those rules on their own. This page covers the setout maths only.

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 about 180 mm. That riser height feels right for most people.

2700 ÷ 180 = 15 risers exactly.

What if the split is not a whole number? Round to the nearest whole number of risers. Then divide the total rise by that count. Your riser height shifts a few mm from the target. The shift spreads evenly across every step. That is what you want.

2. Work out the treads. Always one fewer than the risers. The top and bottom risers land you on a floor, not a tread.

15 − 1 = 14 treads.

3. Choose a going. Pick 280 mm. That is a common tread depth, and it feels right underfoot.

4. Check it against 2R + G.

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

That sits inside the 600–650 mm comfort range. The stair will feel right to climb. Not cramped, not a stretch.

So: 15 risers at 180 mm, and 14 treads at 280 mm. The comfort check comes out at 640 mm. Now you can start marking the stringer.

Do it in 5 seconds

Each country sets its own legal riser and going limits, on top of the comfort maths here:

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. Each riser lands a few millimetres from your target, spread evenly.
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 around 600–650 mm, close to an average adult stride. Land inside that range and the stair feels natural to climb. Too far under feels cramped and steep. Too far over is 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 comfort check.