Stair Calculator
Work out riser height, tread depth and the number of steps for your staircase with this free stair calculator that runs in your browser.
Stair inputs
Ranges are guide values (reviewed 2026-06-23). Confirm the current NCC / building code and the situation — this is not a compliance certificate.
Result
| Risers | Riser | 2R+G | Run | Status |
|---|---|---|---|---|
| 13 | 207.7 | 665 | 3,000 | Fail |
| 14 | 192.9 | 636 | 3,250 | Fail |
| 15 | 180 | 610 | 3,500 | Pass |
| 16 | 168.8 | 588 | 3,750 | Pass |
| 17 | 158.8 | 568 | 4,000 | Pass |
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the total rise (floor-to-floor), a target riser and a going.
- Read the recommended riser count, actual riser, 2R+G, pitch and total run.
- Compare nearby riser counts in the options table, and edit the guide ranges if your code differs.
How it works
The riser count starts at round(total rise ÷ target riser); the tool also tests counts either side so you can see better options. The actual riser = total rise ÷ riser count.
The slope relationship 2R + G (twice the riser plus the going) is the comfort check. For a floor-to-floor flight ending on a landing or upper floor there is one fewer going than risers, so the total run = going × (risers − 1).
Worked example
2,700 mm rise, 180 mm riser, 250 mm going. 15 risers of 180 mm; 2R+G = 360 + 250 = 610 mm; 14 goings give a 3,500 mm total run. 14 risers would be 192.86 mm — over a 190 mm guide maximum.
Common mistakes
- Counting goings as equal to risers — a floor-to-floor flight usually has one fewer going.
- Picking a riser without checking 2R+G — the riser and going can each be in range yet feel wrong together.
- Treating the guide ranges as compliance. The real limits depend on the current code and the building class.
Frequently asked questions
What is 2R+G?
Twice the riser height plus the going. It's a long-standing comfort rule; many codes keep it within roughly 550–700 mm.
How many risers do I need?
Start with round(total rise ÷ your target riser), then check the actual riser stays in range. The options table shows the counts either side.
Is the total run the risers or the goings?
The run is built from goings. A floor-to-floor flight has one fewer going than risers, so run = going × (risers − 1).
Does this certify my stair to code?
No. It checks editable guide ranges only. Confirm riser, going, 2R+G, headroom, handrails and landings against the current NCC / building code for your project.
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Cite this tool
Zerdly. (2026). Stair Calculator. Retrieved from https://www.zerdly.com/tools/stair-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.