ISO 717-2:2013: 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 140-7, and in octave bands in accord-ance with that option in ISO 140-7 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 ISO 717-2:2013 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 an annex. A method for obtaining single-number quantities for bare heavy floors according to their performance in combination with floor coverings is described in a second annex. An example of the calculation of a single-number quantity is given in a third annex.