How to work out stair riser and going dimensions
Comfortable stairs come down to one rule: every riser must be the same height.
People trip when one step differs from the rest by even a few millimetres, because your feet get used to the rhythm after the first couple of steps. Start with the exact total rise, measured from the finished floor below to the finished floor above, then divide it evenly.
Step by step
Measure from finished floor to finished floor, allowing for floor coverings like tiles or carpet that aren't laid yet.
About 175 mm is comfortable. Round the result to a whole number of risers.
Total rise ÷ number of risers. Every step will be this height.
The going is the tread depth, measured from one nosing to the next. Twice the riser plus the going should land within 550–700 mm for a natural stride.
Number of goings = risers − 1, because the upper floor acts as the last tread. Total run = goings × going.
Worked example: 2,700 mm floor to floor
| Item | Calculation | Result |
|---|---|---|
| Risers | 2,700 ÷ 175 = 15.4, round to | 15 |
| Riser height | 2,700 ÷ 15 | 180 mm |
| Goings | 15 − 1 | 14 |
| Going | Chosen | 250 mm |
| 2R + G | 2 × 180 + 250 | 610 mm ✓ |
| Total run | 14 × 250 | 3,500 mm |
When the run doesn't fit
If 3,500 mm of run won't fit the space, you can use fewer, taller risers (within the limits), shorten the going, or add a landing and turn the stair. Each of these changes the numbers, so run the calculator again after any change.
✨ Key Takeaways
- Every riser must be identical.
- There's one fewer going than risers.
- Check 2R + G lands within 550–700 mm, and confirm the NCC limits with your certifier.