It takes anywhere from three to 24 hours for a refrigerator to reach safe temperatures for storing food, depending on the size and type of unit. When the refrigerator compartment reaches 40 degrees Fahrenheit and the freezer reaches 5 degrees Fahrenheit, it is safe to transfer food items.
Checking the temperature is the only way to be sure a refrigerator has cooled enough for safe food storage. A thermometer placed in a glass of water in the center of both the freezer and refrigerator compartments provides an accurate measurement of their temperatures. Refrigerators need to be between 37 to 40 degrees Fahrenheit, and freezers are ideally between 0 and 5 degrees Fahrenheit. Some contemporary computerized refrigerators provide a digital display of the temperature of each compartment.