Liquid crystal cells have always been an important part of commercially available displays, modulators and projectors. In this paper, Jones matrix representation including four independent parameters for twisted nematic liquid crystal (TN-LC) cell has been demonstrated. The physical parameters of the TN-LC cell such as twist angle, birefringence and director orientation at the input face of cell has been calculated using intensity transmittance of an experimental set-up that includes circularly polarized light and TN-LC cell sandwiched between two polarizers. The physical parameters have been calculated without any ambiguity using three different wavelengths.The knowledge from above measurement gives the general information about the birefringence and hence liquid crystal cell gap thickness. To acquire full-field liquid crystal cell gap thickness measurement phase shift polariscope has been adopted. The four phase shifted images through the rotating analyzer gives the full-field cell gap thickness measurement. The experimental results have been compared with the commercial point wise measurement and are in good agreement.