This part of ISO 717: a) defines single-number quantities for impact sound insulation in buildings and of floors; b) gives rules for determining these quantities from the results of measurements carried out in one-third-octave bands in accordance with ISO 10140-3 and ISO 16283-2, and in octave bands in accordance with that option in ISO 16283-2 for field measurements only; c) defines single-number quantities for the impact sound reduction of floor coverings and floating floors calculated from the results of measurements carried out in accordance with ISO 10140-3; d) specifies a procedure for evaluating the weighted reduction in impact sound pressure level by floor coverings on lightweight floors. The single-number quantities in accordance with this part of ISO 717 are intended for rating impact 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 rating of results from measurements carried out over an enlarged frequency range is described in Annex A. A method for obtaining single-number quantities for bare heavy floors according to their performance in combination with floor coverings is described in Annex B. Examples of the calculation of a single-number quantity is given in Annex C. A method for rating heavy/soft impact sound insulation performance of building and building materials by A-weighted maximum impact sound pressure level is given in Annex D.