Free NZ stair calculator. Equal risers from a total rise, with the going, run, stringer length and pitch, or fit a flight to a fixed run. Verify against D1/AS1.
This calculator divides a total rise into equal risers and gives you the going, the run, the stringer length and the pitch. It works two ways: pick the going and let the run fall out of it, or fix the run and let the going be solved from it. It sets out a flight. It does not decide whether that flight is acceptable, and the difference is deliberate.
Give it the finished floor to finished floor rise, the largest riser you want, and your going, and it back-solves the number of risers that divides the rise evenly.
That even division uses the same solver CostMate's estimating engine uses for balustrade post spacing, because it is the identical problem: a run that must not end in a stub. Seventeen risers at 176.5mm for a 3000mm rise, never sixteen at 180mm plus one odd 120mm step, which is the classic way a flight ends up dangerous.
The run is the going multiplied by the number of goings, and whether that is one fewer than the risers depends on whether the top step is the upper floor itself. That is the switch on the page, and getting it wrong is the other common set-out error.
The stringer length is the hypotenuse of the run and the rise, and the pitch follows from the same triangle. The page also shows the flight with one more riser and one fewer, so you can see what a slightly different set-out would cost you in run.
The second tab is for the case where the landing spot is already decided: the edge of a path, an existing slab, the end of a hallway. There the run is a constraint, not an output, and asking you for a going is the wrong question: the flight has to climb a known height inside a known distance.
Give it the rise and the run and it solves the going instead, as the run divided by the number of treads. Everything else follows from the same triangle.
One thing worth knowing about this mode: with both the rise and the run pinned there is only one slope, so the stringer length and the pitch are identical for every riser count. Changing the riser count moves the riser height, the going and the counts, and never the stringer. The alternatives on the page show the going rather than the run for exactly that reason.
The riser count is still driven by the maximum riser you type in, in both modes. Once the rise, the run and the riser count are fixed there is no freedom left in the going, so the only judgement in the second mode is how many risers, and that stays on your figure rather than one of ours.
It does not state a maximum riser, a minimum going, or an acceptable band for two risers plus a going. It reports the two-risers-plus-going value and never a range, because the range belongs to D1/AS1 and this tool does not source it.
That is the same line CostMate takes inside the app, where the stairs option flags a D1/AS1 access-route scope check (going, riser, handrail, landing) and asks you to verify the dimensions rather than asserting them for you.
The maximum riser field is your target, not a limit CostMate is setting. Put in the figure you are working to.
Riser, going, handrail and landing dimensions are design decisions. Verify them against current D1/AS1 and your plans, and measure finished floor levels rather than framing, before you cut a stringer.