A maximum relative variation of the reverberation time according to the size of the audience must be stated as a design condition for a hall together with the value of the reverberation time itself (for instance, 1.3 sec at 500 cps, ±10%). It is interesting and very useful to compute, quantitatively, how a change in the type of seats, the volume of the hall, or the number of seats would affect the relative variation in the reverberation time according to the number of occupied seats. The present work gives, in the form of equations and charts, an easy way to do this.