Does larger graphite flake size always lead to larger and better graphene oxide (GO)? Is there an optimum size to balance between the large building blocks needed and the defects generated during oxidation? In this study, the effect of using four different graphite flake sources on the size, structure, and properties of GO and reduced graphene oxide (rGO) was investigated. GO was mainly prepared by the enhanced synthesis method except for the smallest graphite size, which could not be expanded before oxidation. The effect of the flakes' lateral size and thickness on the expansion volume was also studied. Several characterization techniques were performed throughout this work, and their results provide evidence of how the graphite size changes not only the expansion volume of the chemically expanded graphite (CEG) as well as the final properties of GO or rGO but also the presence of organosulfate impurities, defects, wide size distribution, and the harsh oxidation reaction itself.