A method for charging a field refrigeration system including an evaporator, a condenser, a compressor, and an expansion device includes calculating a target superheat as a function of one or more of a measured field outdoor dry bulb temperature, and a measured field indoor wet bulb temperature. A charge adjustment percentage can be calculated as a function of the target superheat. A refrigerant adjustment weight can be determined based on the charge adjustment percentage. A field refrigeration system charge can be adjusted by the refrigerant adjustment weight.