Sound level difference between two rooms depends on both sound reduction between the rooms and their acoustical properties, such as the absorption in the receiving room. In order to abstract the influence of the rooms and assess only the sound reduction between them, relevant building acoustics standards offer two ways of normalizing a measured sound level difference – according to the reverberation time and the equivalent sound absorption area in the receiving room. In both cases measurement procedure requires reverberation time measurements in the receiving room, from which the equivalent sound absorption area can be assessed using Sabine’s formula. This paper analyses more than 300 results of reverberation time field measurements and provides an insight into its typical values in buildings. The measurements are done by five teams of building acoustics engineers, mostly involved in the international EU COST Action TU0901. The results are gathered in a unique database as a part of the STSM (Short Term Scientific Mission).