A draft standard was presented by a working group within ISO in April 2011. It describes six methods to simplify the measurement of a spatially averaged sound pressure level in a room, in order to determine an airborne sound insulation between two rooms. The draft standard is intended to replace ISO 140 part 4. The proposed methods are based on various spatial sampling techniques, where a microphone is moved continuously or kept steady at ?xed positions in differ¬ent parts of the room. The uncertainty of the average is to a large extent related to the ability of the sampling method to sample sound pressure levels uniformly from all parts of the room. The uncertainties of the simpli?ed methods of the draft standard have been estimated empirically by means of measurements made in ?ve rooms with different acoustic conditions. The result of each type of simpli?ed method is compared to an average of sound pressures recorded in a dense mesh of microphone positions throughout the permitted space in the same room. Some results that may be useful when an averaging method is to be decided: • the standard deviations may actually be higher above 100 Hz than below, the 160 and 200 Hz third octave bands may even contain the most uncer¬tain results • the ?xed positions method is practical and may be used in all types of room • the special corner method gave higher average sound pressure levels and lower uncertainties compared to the other methods • moving microphone methods are dif?cult to apply in small furnished rooms where there is not enough space to complete several indepen¬dent microphone paths • moving microphone methods may be sensitive to operator generated background noise • microphone positions should be spread over the entire room volume. This study has not estimated the uncertainty of the sound pressure level differ¬ence between two adjacent rooms, used for sound reduction index estimates.