This International Standard provides a method for calculating percentiles of the hearing threshold distribution whose mean is the reference threshold value specified in ISO 226 and ISO 389-7. The mean and percentile thresholds are specified under the following conditions: a) the sound field in the absence of the listener consists of a free progressive plane wave (free field); b) the sound source is directly in front of the listener (frontal incidence); c) the sound signals are pure (sinusoidal) tones; d) the sound pressure level is measured in the absence of the listener at the position where the centre of the listener's head would be; e) listening is binaural; f) the listeners are otologically normal persons within the age limits of 18 years to 25 years inclusive. NOTE The applicability of the percentiles and the values of parameters given in this International Standard to diffusefield listening conditions has not been examined. They are expected to be applicable to the conditions for the frequencies from 20 Hz to 250 Hz where the threshold difference between free-field and diffuse-field listening conditions is zero as specified in Table 1 of ISO 389-7:2005. The percentiles are given in numerical form for the preferred frequencies in the one-third-octave series from 20 Hz to 16 000 Hz inclusive, in accordance with ISO 266 and for some intermediate audiometric frequencies.