If the peak impeller and diffuser efficiencies are prescribed, it is found that the characteristics of high-speed radial compressors with straight radial blades are basically functions of the inducer and diffuser throat areas. Estimated characteristics for twenty-seven compressor geometries are presented to indicate the effects of inducer blade angle, diffuser throat to impeller inlet area ratio, and impeller tip to inducer RMS diameter ratio. The probable location of compressor surge as influenced by inducer and diffuser blade stalling is discussed, and comparisons of estimated and test compressor characteristics are given.