Building
Stair Calculator
Risers, going and stringer length with an instant NCC compliance check.
Guide only. Verify against the NCC and your local council requirements, and consult a licensed builder before constructing stairs.
How this calculator works
Enter your total rise, the vertical height the stairs must climb, and the calculator divides it by an ideal riser of 178mm, rounding to a whole number of risers. Every riser must be identical, so it then splits your rise evenly.
If you enter the total run available, the going of each tread is calculated from it. Otherwise a comfortable 280mm going is assumed. Stringer length comes from Pythagoras on the total rise and run.
Your numbers are checked live against the National Construction Code limits for private stairs: risers 115mm to 190mm, goings 240mm to 355mm, and the comfort rule of two risers plus one going between 550mm and 700mm.
| Measure | Minimum | Maximum |
|---|---|---|
| Riser height (R) | 115mm | 190mm |
| Going (G) | 240mm | 355mm |
| 2R + G | 550mm | 700mm |
| Headroom | 2,000mm vertical | no maximum |
Class 1 buildings (houses). Public and commercial stairs have tighter rules. Landings are required every 18 risers.
| Total rise | Risers | Riser height | Suggested going |
|---|---|---|---|
| 1,000mm (deck) | 6 | 166.7mm | 280mm |
| 2,400mm | 14 | 171.4mm | 280mm |
| 2,700mm (standard ceiling) | 15 | 180mm | 280mm |
| 3,000mm | 17 | 176.5mm | 280mm |
Frequently asked questions
How do I measure total rise?
Measure vertically from the finished lower floor to the finished upper floor, including any floor coverings. Getting this measurement right matters because every riser must come out identical.
What is a comfortable riser height and going?
Around 175mm risers with a 280mm going feels natural for most people, and satisfies the NCC comfort rule where two risers plus one going should total 550mm to 700mm.
Do all steps have to be the same height?
Yes. The NCC allows very little variation between risers in a flight because uneven steps cause trips. This is one of the most common defects flagged in building inspections.
How many steps before I need a landing?
The NCC requires a landing after no more than 18 risers in a single flight. Most homes never hit that limit: a standard 2.7m floor to floor height needs only 15.
Does an outdoor deck stair follow the same rules?
Yes, deck stairs at a house are covered by the same NCC private stairway limits, and they also need slip resistant treads in most cases.
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