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Stair Rise & Run Setout: Riser, Going & the 2R+G Formula

Calculate straight-flight stair geometry from total rise, riser count and going, with a worked example and a 2R+G check.

Scope: Geometry and quantity estimates only; use the adopted code and approved design for requirements.

Worked arithmetic checked . Review method.

The method

Riser = total rise ÷ number of risers. For one straight flight with the upper floor as the final tread, goings = risers − 1. The going (G) is the horizontal distance from one nosing to the next. Calculate 2R + G and compare it with any range set by the adopted rules.

Some codes, including the Australian Housing Provisions, regulate 2R+G as well as riser and going dimensions. Check the applicable requirements together; a comfortable example alone does not establish compliance. 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. Use 180 mm as the target for this example. It is an input, not a prescribed height.

2700 ÷ 180 = 15 risers exactly.

What if the split is not a whole number? Try whole-number counts on either side, then divide the rise by each count. Check the resulting riser height and run against the approved design and local limits.

2. Work out the treads. In this straight-flight example, with the upper floor as the final tread, there is one fewer going than risers. The top and bottom risers land you on a floor, not a tread.

15 − 1 = 14 treads.

3. Choose a going. Use 280 mm for this example. Check the chosen going against the local limits and available run.

4. Check it against 2R + G.

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

This gives the value to compare with the rule for your project. It does not check the other stair dimensions or guarantee comfort.

So: 15 risers at 180 mm, and 14 treads at 280 mm. The 2R+G calculation comes out at 640 mm. Check the adopted requirements, available run, headroom and approved details before marking the stringer.

Calculate and keep your working

Use the free web tool or download the Chippy Tools printable reference.

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

Sources

The worked example uses division and multiplication. For the Australian housing limits on 2R+G, see the NCC stair guide and its linked official provision. Other countries and building types can set different limits.

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 a target riser height gives a fractional count, try whole-number counts and divide the total rise again. Check each result against the rules and available space.
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?
Add twice the riser height to one going, using the same units. For R = 180 mm and G = 280 mm, 2R+G = 640 mm. Some codes set limits for this value. It cannot establish comfort or compliance on its own.
How many treads does a staircase have?
For a straight flight with the upper floor acting as the final tread, there is one fewer going than 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?
There is no single pair that suits every user or stair. A 180 mm riser and 280 mm going give 2R+G = 640 mm in this example. Choose dimensions that meet the adopted rules, approved design and available space.