What this calculator does
Stairs are set by the total rise, which cannot change, so the target riser height is only a starting point. A 260 cm rise with a target of 18 cm gives 14 steps at an actual 18.57 cm, because 260 does not divide evenly.
The comfort rule is that twice the riser plus the tread should land between 60 and 65 cm. This staircase gives 64.1 cm and passes. It encodes something real about how people walk: a taller riser needs a shallower tread to keep the stride natural, and getting the balance wrong makes a staircase tiring in a way that is hard to put a finger on.
The formula
The step count is the total rise divided by the target riser, rounded to the nearest whole number. The actual riser is then the total rise divided by that count, which is why it rarely matches the target. Total run is the steps less one multiplied by the tread depth, and the stringer is the diagonal across the whole flight.
| Term | Meaning |
|---|---|
| Rise | Total floor-to-floor height, which is fixed by the building. |
| Riser | The height of one step. All risers in a flight must be equal. |
| Tread | The depth of one step, front to back. |
| Stringer | The sloping board carrying the steps, whose length is the flight diagonal. |
The inputs explained
| Field | What to enter |
|---|---|
| Total floor-to-floor rise (cm) | Total floor-to-floor rise in centimetres, including floor finishes at both levels. |
| Target riser height (cm) | Target riser height. The actual will differ, since the rise must divide into whole steps. |
| Tread depth (cm) | Tread depth. Deeper treads suit shallower risers. |
When to use it
Designing a staircase
The step count and actual riser are the first figures to settle, and everything else follows from them.
Checking an existing flight
Measuring an uncomfortable staircase against the comfort rule usually explains why it feels wrong.
Planning the space needed
The total run determines how much floor a staircase consumes, which is often the binding constraint.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does the target riser change the flight?
The same rise divided by a range of target riser heights.
| Target riser | Number of steps | Actual riser height | Comfort check (2×riser + tread) |
|---|---|---|---|
| 16 cm | 16 | 16.25 cm | 59.5 cm: outside the usual 60–65 cm comfort range |
| 17 cm | 15 | 17.33 cm | 61.7 cm: comfortable |
| 18 cm | 14 | 18.57 cm | 64.1 cm: comfortable |
| 19 cm | 14 | 18.57 cm | 64.1 cm: comfortable |
| 20 cm | 13 | 20.00 cm | 67.0 cm: outside the usual 60–65 cm comfort range |
Questions
Why is the actual riser different from my target?
Because the total rise must divide into a whole number of equal steps. A 260 cm rise with an 18 cm target gives 14.4 steps, which rounds to 14, and 260 divided by 14 is 18.57. The target only selects the step count.
What is the stair comfort rule?
Twice the riser plus the tread should fall between about 60 and 65 cm. It reflects natural stride length: a taller step needs a shallower tread. Staircases outside the range feel cramped or stretched even when each dimension seems reasonable alone.
Must all the risers be equal?
Yes, and this is a genuine safety matter rather than a preference. People climb stairs without looking, and a single riser differing by even a centimetre causes trips. Building codes require uniformity within a few millimetres across a flight.
How much floor space will the stairs need?
The total run figure, which for this example is 351 cm. Steeper stairs use less floor but are harder to climb and may not meet code. Building regulations set maximum riser and minimum tread dimensions, which cap how steep you can go.
For railing spindles, see the baluster spacing calculator. For a ramp instead, see the ramp slope calculator.