Abstract — The concept of linking pore-scale data to continuum-scale characteristics of porous media relies on the existence of a representative elementary volume (REV). The current techniques for estimating REVs requires access to segmented micro-tomographic (micro-CT) images and computations of petrophysical properties which are computationally intensive and time-consuming. Herein, a texture characterization method called the Gray-Level Size-Zone Matrix (GLSZM) is applied directly to raw grayscale micro-CT images. GLSZM representations of 3D micro-CT images capture information regarding the connectivity of gray-level intensities, termed as ‘size-zones’. Statistical descriptors of pore-space are calculated based on GLSZM to understand the connectivity of low gray-level intensities. These GLSZM statistics capture microstructural fluctuations and offer insights into the impact of grayscale heterogeneity on REV size. This approach allows REV sizes to be estimated directly using grayscale micro-CT images, in a reproducible, less time consuming and computationally efficient manner.