What is the difference between clear room height and floor-to-floor height?

These two measurements are often confused, but both are important for staircase planning:

Clear room height: The vertical distance between the finished floor of a storey and the underside of the ceiling. It describes the actually usable interior space and is needed to check whether sufficient headroom (at least 2 m) is available.

Floor-to-floor height: The height difference from the top of the floor of one storey to the top of the floor of the storey above. It includes the clear room height plus the thickness of the ceiling (structural slab + screed + floor covering).

For calculating the number and height of risers, the floor-to-floor height is used, because the staircase runs from finished floor to finished floor. The thicker the ceiling, the greater the difference between room height and floor-to-floor height. During the survey, HTS records both values precisely.