Joule-Thomson (J-T) refrigerators/cryocoolers, also known as Linde-hampson refrigerators, operating with mixtures, are widely used in various ultra-low-temperature applications. The cooling capacity of a J-T refrigerator depends on several factors, such as the mixture composition, expansion capillary tube geometry, and the heat exchanger's design. The main goal of the proposed work is to estimate the cooling capacity of a Mixed Refrigerant J-T (MRJT) refrigerator for the specified hardware and mixture prior to experimentation. An iterative steady-state full-cycle simulation method has been developed to evaluate the cooling capacity. The effects of mixture composition, heat exchanger geometry, expansion capillary geometry, and choking on the cooling capacity have been studied. The results of these studies will be presented in this work.