Rock geo-mechanical properties are important in petroleum engineering. The determination of reservoir’s mechanical properties is critical to reduce drilling risk and maximizing well and reservoir productivity. Rock geo-mechanical properties vary not only with rock types, but also with measurement method, samples geometry (sample size and length to diameter ratio), and other factors. Because rocks are heterogeneous media, sample geometry can significantly affect measured rock mechanical properties, including unconfined and confined compressive strength, Young’s Modulus, and Poisson’s ratio. In this study, uniaxial compressive tests were conducted on 31 different dimensions of Berea sandstone samples to study the geometry effects on rock geo-mechanical properties. The objective of this research is to provide a fundamental understanding of the geometry effects. Correlations equations were established and standardizing factors were generated to minimize the geometry effects and get more reliable rock mechanical properties. Failure mode of the tested samples was also studied in this work.