A refrigeration system includes a refrigerant vapor compression unit including a compressor and one or more current sensors to determine a total system current draw. One or more pressure sensors are positioned to determine a refrigerant pressure in the refrigerant vapor compression unit. A controller compares the current draw on the system and the refrigerant pressure to selected acceptable ranges and determines a level of refrigerant charge in the refrigerant vapor compression unit. A method of determining a level of refrigerant charge in a refrigeration system includes measuring a refrigerant pressure in the refrigeration system and sensing a current draw of the refrigeration system. A level of refrigerant charge in the refrigeration system is calculated from the refrigerant pressure and the current draw.