Physical size reduction of biomass through mechanical means is a necessary step in bioconversion of lignocellulosic materials to increase the substrate surface accessible to enzymes to achieve a satisfactory cellulose conversion efficiency.  Unfortunately, reducing biomass size to the scale of sub to millimeter requires a significant amount of electric-mechanical energy, especially for woody biomass.  It is estimated that the energy consumed in size reduction can be 30-65% of the total energy in the cellulose ethanol produced using current technology (assume 35% conversion efficiency of thermal to electrical energy).  Most literature studies reported cellulose conversion efficiency without providing the substrate size and size reduction energy consumption, while other studies provided the substrate size and size reduction efficiency but without the cellulose conversion efficiency.  In this study we took an integrated approach to relate size reduction process to cellulose conversion efficiency and size reduction energy consumption.  This presentation demonstrates a methodology for correct shape and size characterization of substrate so that a valid comparison of the effectiveness of size reduction, chemical pretreatment, and enzymatic hydrolysis process can be made.  Since lignocellulosic substrates have a very large aspect ratio, measurements of geometric length using traditional sieving or screening methods reported in the literature were unable to provide correct information about enzyme accessibility.  The correct definition of substrate size is critical to identify the most efficient size reduction, chemical pretreatment and enzyme process for biomass bioconversion.  Our results demonstrated that the developed methodology is effective to differentiate the efficiencies of different size reduction processes.