Auxetic materials with a negative Poison's ratio (PR) have the potential to meet the demand for different materials, especially technical textiles. Universal Tensile Test (UTT) devices and various experimental setups developed by researchers have been used in PR measurements. This study aims to investigate the PR of knitted fabrics with UTT and extensometer devices comparatively by using the same measurement parameters according to ASTM E132. Knitted fabrics with zigzag and foldable patterns were produced in the study because of their auxetic behaviour. It has been determined that the extensometer device can be used as an alternative to the UTT device for PR measurements. While the PR of foldable fabrics cannot be measured with the UTT device because of the fabrics' folding on themselves, it has been observed that it can be easily measured with the extensometer device thanks to the horizontal axis principle.