Take the temperature of a refrigerator with a bulb-style or candy thermometer, recommends General Electric. Place the thermometer on the middle shelf in food or liquid that has been in the refrigerator for no less than 24 hours. After at least three minutes, check the temperature.
A refrigerator's temperature should be between 34 and 42 degrees Fahrenheit, notes GE. Pick up a refrigerator thermometer at a hardware or grocery store and leave it in the appliance to ensure a proper temperature in continually maintained, suggests Jeannie Nichols for Michigan State University Extension.
If a refrigerator is too cold, food is likely to freeze. Sometimes this is just inconvenient, but other times the quality of food suffers. For instance, when frozen lettuce thaws, it is wilted and soggy, states Tim McKeough for The New York Times. If the temperature is too high, harmful bacteria thrive. When contaminated food is eaten, people sometimes become ill, observes Nichols.
Measuring the temperature of the freezer portion of the refrigerator is a similar process. The same type of thermometer is used, as long as its scale goes below zero degrees Fahrenheit, advises GE. Place the thermometer in the middle of the freezer section between packages of food for three minutes. Optimal freezer temperatures are between minus 5 degrees Fahrenheit and 8 degrees Fahrenheit.