A large database of values of various room acoustic parameters has provided the basis for statistical analyses of how and how much the acoustic properties of concert halls are influenced by their size, shape, and absorption area (as deduced from measured reverberation time). The data have been collected over a 15-year period from about 50 concert halls in Europe and the U.S. In all halls the same measurement technique was used (1/1 oct sweep tones all pass filtered to form impulse responses per octave band). Due to the large range of geometric differences contained in the material, it has been possible to derive empirical regression formulas from which the influence of certain geometrical design variables can be quantified. The author has found these fairly simple relationships useful in teaching and as guidelines both in the early stages of physical hall design and in setting up electronic reverberation enhancement systems.