Stairs Calculator — Steps and Dimensions 2026

The number of steps is found by dividing the floor-to-floor height by the target riser height and rounding to a whole number. With a height of 280 cm and a target riser of 17 cm you get 280 / 17 ≈ 16.5, i.e. 16 risers. The actual riser height is then 280 / 16 = 17.5 cm.

In residential construction a comfortable riser height is 15–19 cm. Polish technical conditions for single-family buildings allow a maximum riser of 19 cm and a minimum tread of 25 cm. The most comfortable stairs have risers of 16–18 cm.

The Blondel rule (comfortable stairs formula) describes the relationship between riser and tread: 2 × riser + tread = 60–65 cm. It is based on the natural length of a human step. Stairs that meet this condition are safe and comfortable — too low a value means sprawling stairs, too high means steep ones.

The tread depth (the surface the foot rests on) should be at least 25 cm, ideally 28–32 cm. It is calculated by dividing the run length by the number of steps minus one (treads = steps − 1). A tread that is too shallow is dangerous when descending.

The horizontal run of the staircase depends on the number and depth of treads. With 16 steps and a 28 cm tread the run is about 15 × 28 = 420 cm. Single-flight stairs need more length; two-flight stairs with a landing save space but require a wider stairwell.

A step is the whole part of the staircase you stand on — it consists of a tread (the horizontal surface) and a riser (the vertical part, i.e. the step height). The number of risers is always one more than the number of treads, because the top riser ends at the level of the upper floor.

According to Polish technical conditions the minimum usable width of a flight in a single-family house is 80 cm, with 90–100 cm recommended. Common stairs in multi-family buildings must be at least 120 cm wide. Narrow stairs make moving furniture difficult.

The calculator computes single-flight stairs (a straight run without a landing). For two-flight stairs with a landing, split the floor height between the two flights and calculate each separately. The landing should be at least as deep as the flight width, a minimum of 80 cm.

The target riser height is the value you aim for when designing. Homes usually use 17 cm, attic or basement stairs up to 19 cm, and representative stairs 15–16 cm. The calculator adjusts the actual height so that all steps are equal.

Results are indicative and serve for preliminary stair planning. The final design should be made by a qualified designer or structural engineer, taking into account applicable technical conditions, material (wood, concrete, metal), load capacity and the individual stairwell dimensions.