The preferred temperature is somewhere between 35 and 38 degrees F (1.7 to 3.3 degrees C). 18°C.
The FDA advises that you should keep the temperature of your fridge between 32 and 40 degrees Fahrenheit, preferably right in the middle of that range, at, say, 35 degrees. Set the temperature at 35, and you avoid the risk of frozen food (that’s what the freezer’s for!) and you avoid the risk of spoilage. That said, this does not mean the temperature inside your fridge will be uniformly 35; temperatures can vary depending on the part of the fridge.  1 Fridge: put the thermometer in a glass of water. 2  Check the temperature during the first door opening after not using the fridge for 8 hours or more (such as overnight). 3  Freezer: put thermometer between two bags of vegetables and as above check after 8 hours or more. 1 A fridge should have a temperature of between 37°F(3°C) and 40°F (5°C). 2  Any higher and the food will go off, any lower and you’ll lose nutrients and fresh food can be ruined. To measure the temperature: 1  Fridge: put the thermometer in a glass of water. 2  Check the temperature during the first door opening after not using the fridge for 8 hours or more (such as overnight). 3  Freezer: put thermometer between two bags of vegetables and as above check after 8 hours or more. 1 A fridge should have a temperature of between 37°F(3°C) and 40°F (5°C). 2  Any higher and the food will go off, any lower and you’ll lose nutrients and fresh food can be ruined. Freezer temperature should be maintained at minus 18°C. (Ice cream is a good indicator of freezer temperature: it should be firm.) Consult your fridge manufacturer's manual for advise on temperature control. Try not to keep opening the fridge door every few minutes. Various Answers The refrigerator should be at about 35°F (1.6°C) which is above freezing, so your milk won't freeze. The refrigerator should be set between 40°F and 34°F (~4.4°C to 1.1°C). The closer it gets to freezing (32°F or 0°C), the longer the food will keep. 1 Keep the refrigerator temperature at or below 40° F (4° C). 2  The freezer temperature should be 0° F (-18° C). 3  Check temperatures periodically. 4  Appliance thermometers are the best way of knowing these temperatures and are generally inexpensive. 1 Also, when putting food away, don't crowd the refrigerator or freezer so tightly that air can't circulate. 2  Keep your appliances at the proper temperatures. 3  Keep the refrigerator temperature at or below 40° F (4° C). 4 1 If you do lose power, keep the doors to your fridge and freezer closed as much as possible to keep foods cold. 2  Before using any foods, check your refrigerator and freezer thermometers. 3  If the fridge is still at or below 40 °F, or the food has been above 40 °F for only two hours or less, it should be safe to eat. When it comes to protecting yourself and your family from foodborne illness, one of your most effective tools is the kitchen refrigerator. In fact, at room temperature, the numbers of bacteria that cause foodborne sickness can double every 20 minutes! 2. Place the thermometer inside a glass of water, and put the glass on your refrigerator's middle shelf. 3. Check the temperature on the appliance thermometer after 5 to 8 hours. The temperature should register between 38 F and 40 F (2 C to 4 C) for safe food storage. 1  Make sure that your thermometer is safe to put in water; not all are Therefore, you want your refrigerator to be cold, but not so cold that it freezes things. The preferred temperature is somewhere between 35 and 38 degrees F (1.7 to 3.3 degrees C). Anything higher and foods will spoil too quickly (it also presents food poisoning problems, as described in several of the links below).  In order to keep food out of the Danger Zone, your fridge must be set between 32-40° F (0-4 degrees Celsius). Your freezer must be below 32° F (0° Celsius). I keep mine as cold as it will go. Keep your freezer efficient by half-filling it with bottles of water. 
http://www.digitaltrends.com/home/what-temperature-should-my-fridge-be/ http://www.knowhow.com/article.dhtml?articleReference=786 http://www.knowhow.com/article.dhtml?articleReference=786 http://www.answers.com/Q/What_is_the_proper_temperature_for_a_refrigerator http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm093704.htm http://www.fda.gov/Food/ResourcesForYou/Consumers/ucm253954.htm http://www.wikihow.com/Set-Your-Refrigerator-Temperature http://home.howstuffworks.com/appliances/energy-efficient/question121.htm http://lifehacker.com/what-temperature-should-you-keep-your-refrigerator-set-533534221
what should the temp be inside a refrigerator