This European Standard describes a calculation model to estimate the total equivalent sound absorption area or reverberation time of enclosed spaces in buildings. The calculation is primarily based on measured data that characterise the sound absorption of materials and objects. Calculations can only be carried out for frequency bands.This European Standard describes the principles of the calculation model, lists the relevant quantities and defines its applications and restrictions. It is intended for acoustical experts and provides the framework for the development of application documents and tools for other users in the field of building construction, taking into account local circumstances.The model is based on experience with predictions for rooms, such as rooms in dwellings and offices, and common spaces in buildings, such as stairwells, corridors and rooms containing machinery and technical equipment. It is not intended to be used for very large or irregularly-shaped spaces, such as concert halls, theatres and factories.