The flow mechanism that is realized in 3-D depending on the fabric's porosity structure determines the fabric's permeability performance. During the flow movement that happens both in the in-plane and through-plane directions, not only the inter-yarn pore properties but inter-fiber pore properties play a significant role as well. The aim of this study is to offer a new method to identify intra-yarn porosity, which has mostly been neglected during the theoretical studies. In this method, initially the cross-sectional images of the cotton yarn in the fabric were achieved, and then the intra-yarn porosity was predicted via image processing and analysis steps. Besides, intra-yarn porosity was calculated theoretically depending on fiber and yarn parameters. The results that were obtained through the image analysis method and theoretical approaches were compared with the experimental data achieved by using Stereo Investigator. As a result, it was observed that the image analysis method was giving fast, objective, successful and expected results while predicting the intra-yarn porosity.