How this stair calculator works
A flight of stairs has to climb a fixed vertical distance — the total rise, measured from one finished floor to the next — in a series of equal steps. Each step adds one riser (the vertical height you climb) and, except for the very top, one tread (the horizontal surface you stand on). That is why a staircase always has one more riser than it has treads.
To find the step count, the tool divides your total rise by a comfortable target riser height — about 7 inches (18 cm) — and rounds to the nearest whole number of risers. It then divides the total rise by that whole number to get the actual riser height, which is what keeps every step equal. The number of treads is the number of risers minus one. If you give a total run, the tread depth is the run divided by the number of treads; if you leave it blank, the tool estimates the run using a sensible default tread of about 10–11 inches (25–28 cm).
Reference note: typical guidance is a riser of roughly 7–7.75 in (18–19.7 cm), a tread of at least 10 in (25 cm), and a 2R + T value near 24–25 in (61–64 cm). These are general comfort and code conventions only — actual building codes vary by jurisdiction and cover headroom, handrails, nosing and step consistency too. Always verify with your local code and permitting office.
Frequently asked questions
- How many steps do I need?
- Divide your total rise by a comfortable target riser height — about 7 in or 18 cm — and round to the nearest whole number for the riser count; the number of treads is one less. Always confirm against your local building code, which sets the exact limits.
- What is a comfortable riser height?
- Around 7 in (about 18 cm) is comfortable, and many codes cap risers near 7.75 in (about 19.7 cm). This tool splits your total rise into equal risers and flags whether each lands in the typical range. Local codes vary, so verify before building.
- What is the rise versus run of a staircase?
- The rise is the total vertical height the stairs climb between finished floors; the run is the total horizontal distance they cover. Each step has its own unit rise (riser height) and unit run (tread depth).
- What is the 2R + T rule?
- A comfort guideline: two riser heights plus one tread depth should total roughly 24–25 in (about 61–64 cm). Steps that meet it feel natural to climb. The calculator reports your 2R + T value so you can check it.
- Are there code requirements for stairs?
- Yes — codes limit maximum riser height, minimum tread depth, headroom, handrails and step consistency. Common residential guidance is a riser up to about 7.75 in and a tread of at least 10 in, but exact rules vary by jurisdiction, so always check your local code and permits.
- What is tread depth?
- Tread depth is the horizontal distance from the front edge of one step to the next — the part you put your foot on. A common minimum is about 10 in (25 cm). It equals the total run divided by the number of treads.