The micro-CT data based analysis of the knitted fabrics in an undeformed state is the main subject of this paper. Spatial internal structure of weft knitted fabrics is analyzed. Although curvature of the yarns in knitted fabric is high, a precise geometrical measurement of the yarn middle line coordinates and cross-sections in the different places can be obtained in 3D without destructing the observed fabric. The approach, based on X-ray microtomography technique, is proposed for defining structure of the knitted fabric. The paper describes experimental micro-CT procedure and parameters during scans, raw data post-processing and obtaining required geometrical parameters of the glass and steel knitted fabrics. In this study the yarn path, cross-sections shape and size are main scope of interest. Described methodology can be applied for determining knitted fabrics made from different materials, results can be used for further micromechanical modelling.