Stair Calculator
Calculate the number of steps, exact riser height, total run and stringer length for a staircase from the total rise.
How to use this calculator
- 1Measure the total floor-to-floor rise.
- 2Set a target riser height — the calculator rounds to a whole number of even steps and tells you the exact resulting riser height.
How the calculation works
Risers = round(Total rise / Target riser height). Stringer length = √(Total rise² + Total run²)- Total rise
- The full floor-to-floor height the stairs must climb
- Total run
- Treads × tread depth — the horizontal distance the stairs cover
The riser height is always recalculated from the rounded number of risers, not left at your target — this is what guarantees every step is exactly the same height, which building code requires for safety (uneven risers are a leading cause of stair falls).
The stringer is the diagonal structural board the treads and risers attach to; its length is simply the hypotenuse of the total rise and total run, via the Pythagorean theorem.
Worked example
108 in total rise, 7.5 in target riser, 10 in tread
- 1.Risers: round(108 ÷ 7.5) = round(14.4) = 14.
- 2.Actual riser height: 108 ÷ 14 = 7.714 in.
- 3.Treads: 14 − 1 = 13, so total run = 13 × 10 = 130 in.
- 4.Stringer length: √(108² + 130²) = √28,564 ≈ 169.01 in.
Result: 14 risers at 7.714 in, stringer length 169.01 in
The anatomy of a staircase
A staircase is built from a small set of repeating parts, and the terms for them show up throughout the building trade even outside carpentry. The rise is the vertical part of a step, the run is the horizontal part, and a flight’s total rise and total run together describe the size of the vertical gap the stairs need to close.
- Riser — the vertical face of a step, from the top of one tread to the top of the next.
- Tread — the horizontal surface you actually step on.
- Stringer — the diagonal structural board that runs the full length of the staircase and supports the risers and treads — usually two or three per flight, cut in a saw-tooth profile to match the rise and run of each step.
- Nosing — the small overhang where a tread extends slightly past the riser below it, which increases usable foot space without adding to the total run.
- Landing — a flat platform breaking up a long flight, required by most building codes above a certain total rise, and useful for changing the stair’s direction.
Why every riser has to match
Building codes are strict about riser height consistency for a simple reason: the body learns the rhythm of a staircase within the first two or three steps and then stops consciously checking each one. A riser that is even a small amount taller or shorter than the others breaks that rhythm and is a well-documented cause of trips and falls — which is why the calculation always rounds to a whole number of risers first and then spreads the total rise evenly across them, rather than using a fixed riser height that might leave an odd, mismatched step at the top or bottom.
Types of staircases
- Straight flight — the simplest form, running in one direction with no turns — easiest to build and to calculate, and what this calculator models.
- L-shaped (quarter-turn) — turns 90 degrees partway up, usually at a landing, often used to fit stairs into a corner or change direction to suit a floor plan.
- U-shaped (half-turn) — turns 180 degrees, typically with two flights and a landing between them, common where floor space is tight but a straight run would be too long.
- Winder stairs — use pie-shaped treads to turn a corner without a landing, saving space but producing treads that narrow sharply toward the inside of the turn.
- Spiral stairs — wind around a central pole, the most space-efficient option of all, but the narrowest and steepest, typically reserved for secondary access rather than a main staircase.
Comfort, safety, and code — three different things
A staircase can satisfy the legal minimums in a building code and still feel unpleasant to use, which is why designers often lean on an older rule of thumb alongside code minimums, not instead of them: the sum of one riser height and one tread depth should land in a comfortable range, commonly cited as around 17 to 18 inches. Steps outside that range aren’t necessarily unsafe or non-compliant, but they tend to feel unusually steep or unusually shallow to walk.
Code minimums exist for a different reason — they set a floor for safety, not a target for comfort — and they vary by jurisdiction and by whether the stairs are inside a home, in a public building, or on an exterior structure. Maximum riser height and minimum tread depth are the two figures regulated almost everywhere, but the exact numbers should always be checked against the applicable local code rather than assumed from a general guideline.
What this assumes, and where it stops
Assumptions
- A straight staircase with uniform risers and treads throughout — no winders, landings, or variable-width steps.
Limitations
- Does not account for headroom clearance, handrail requirements, or the thickness of finish flooring at top and bottom, all of which building code also regulates.
Common questions
Why is my actual riser height different from what I entered?
You cannot have a fractional number of steps, so the calculator rounds to the nearest whole number of risers and then recalculates the exact height each one needs to be so the total rise comes out exactly right. This is standard practice — a real staircase is always built to a rounded step count with a slightly adjusted riser height, never the other way around.
What is the "comfort" rule for stairs?
A common rule of thumb is that riser height plus tread depth should total around 17–18 inches (or roughly 2× riser + tread ≈ 24–25 in) — steps steeper or shallower than this tend to feel awkward to climb even if they meet minimum code. It is a comfort guideline, not a legal requirement, and it sits alongside (not instead of) your local building code minimums.
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
Related calculators
Tools people commonly use alongside the stair calculator.