Abstract This paper presents the results of a field test program to evaluate and characterize the performance of shredders used for the size reduction of solid waste. In all, tests were conducted on seven horizontal hammermills, one vertical hammermill, and one vertical ring shredder at six commercial sites (Appleton, Wisconsin; Ames, Iowa; Cockeysville, Maryland; Great Falls, Montana; Tinton Falls, New Jersey; and Odessa, Texas). Both two-stage size reduction (Ames) and single-stage size reduction were studied as part of this work. Evaluation and interpretation of the data have resulted in the development of analytical relationships among the comminution parameters, the development of methods for characterizing shredder performance, and the establishment of levels of performance with respect to energy consumption and hammer wear associated with size reduction of solid waste.