How this stair calculator works
Steps need to be even — every riser on a flight should be the same height, or people trip on the odd one out. The calculator takes your total rise and your preferred riser height, works out the nearest whole number of steps, then divides the rise evenly across them. That's why the actual riser height in your result is usually a few millimetres different from what you typed in — it's been rounded to give you whole, equal steps.
- Number of risers: total rise ÷ preferred riser height, rounded to the nearest whole number.
- Actual riser height: total rise ÷ number of risers — always slightly different from your target, and always equal step to step.
- Number of treads: one fewer than the number of risers, since the top riser lands you on the deck or landing itself rather than another tread.
- Stringer length: straight-line distance from the bottom of the first riser to the top of the last, using total rise and total run (Pythagoras) — the length to cut your stringer board before marking out individual steps.
Example: a 900 mm total rise with a 180 mm target riser needs 5 steps at 180 mm risers exactly — a clean number. A 950 mm rise with the same 180 mm target rounds to 5 steps too, but the actual riser height comes out at 190 mm per step instead, since 950 doesn't divide evenly by 180.
What makes a comfortable, safe stair
Australian residential stair guidance (via the NCC Housing Provisions) generally works within these ranges for domestic stairs:
- Riser height: typically 115–190 mm, with 180 mm a common comfortable target for decks and garden steps.
- Going (tread depth): typically 240 mm minimum for domestic stairs.
- Comfort rule of thumb: tradies commonly check that (2 × riser) + going lands somewhere around 550–700 mm — too low feels steep and cramped, too high feels like an awkward stretch with every step.
The calculator checks your result against this rule of thumb and flags it if your combination falls outside the comfortable range, so you can adjust your riser or going before cutting anything.
Stair calculator — frequently asked questions
Why is my actual riser height different from what I entered?
Every riser on a flight of stairs needs to be exactly equal, so the calculator rounds your total rise to a whole number of steps, then divides it evenly. Your actual riser height will usually be a few millimetres different from your target as a result — that's expected and correct.
What's a comfortable riser height for deck or garden stairs?
Around 150–180 mm is comfortable for most people on outdoor steps. Domestic guidance generally allows up to 190 mm, but lower risers with a deeper going tend to feel safer and easier on garden steps in particular, especially if they'll be used at night or by less mobile family members.
How do I work out my stringer length?
Stringer length is the straight-line distance from the base of the first step to the top of the last, calculated from your total rise and total run using Pythagoras' theorem. This calculator works it out automatically — you'll still need to mark out the individual step profile on the stringer board once you've cut it to length.
Do deck stairs need a handrail in Australia?
Generally, a flight of stairs with a total rise over a certain height (commonly around 1 m, but check current NCC Housing Provisions and your council) requires a compliant handrail and balustrade. This varies by state and by the specific circumstances of the build, so check before finalising your design — this calculator doesn't check handrail compliance.
What's the difference between rise, going and stringer length?
Rise is the vertical height of one step (or the total vertical height of the whole flight). Going is the horizontal depth of one tread — where your foot actually lands. Stringer length is the diagonal length of the angled board that supports the steps, running from the bottom of the flight to the top.
Related calculators
These calculators provide estimates for planning purposes only and don't replace professional advice. For structural, waterproofing, electrical or other safety-sensitive work, always check with a licensed tradie before starting your project.