This document a) defines single-number quantities for airborne sound insulation in buildings and of building elements such as walls, floors, doors, and windows, b) takes into consideration the different sound level spectra of various noise sources such as noise sources inside a building and traffic outside a building, and c) gives rules for determining these quantities from the results of measurements carried out in one-third-octave or octave bands for example in accordance with ISO 10140-2 and ISO 16283-1. The single-number quantities in accordance with this document are intended for rating airborne sound insulation and for simplifying the formulation of acoustical requirements in building codes. An additional single-number evaluation in steps of 0,1 dB is indicated for the expression of uncertainty (except for spectrum adaptation terms). The required numerical values of the single-number quantities are specified according to varying needs. The single-number quantities are based on results of measurements in one-third-octave bands or octave bands. For laboratory measurements made in accordance with ISO 10140-2, single-number quantities are calculated using one-third-octave bands only. The rating of results of measurements carried out over an enlarged frequency range is dealt with in Annex B.