Beranek's book Music Acoustics and Architecture (pages 550– 551) gives three curves that allow one to predict the reverberation time for an occupied concert hall from the measured reverberation time for the unoccupied hall. Beranek fitted these curves by eye to his tabulated data (Appendix 2) on the reverberation times measured (at 125, 500, 1000, and 2000 Hz) in approximately 50 unoccupied and occupied halls, built before 1960. This paper presents least-squares regression curves fitted to Beranek's data, establishes the probable reliability of the revised prediction (in terms of correlation coefficients and standard errors of estimates), and extends the prediction to other frequency bands of interest. Comparison with measured data from unoccupied and occupied halls shows good agreement with the predicted values.