Abstract: The determination of the sound power of a source is simple in a reverberation cham-bei, but usually lower values are obtained at low frequencies than the free-space valus. It is shown that the sound power determined in a reverberation chamber depends not only on its free-space power, but also on the positions of the source and the receiver, as well as the way the measurements are made and averaged. Exact and statistical formulas are derived to account for these factors. The results explain the discrepancy and agree well with earlier experiments. Based on the theory, practicable techniques of sound power determination are proposed and correct power formulas presented.