FEVER - Most experts agree that an oral temperature over 99.5 degrees Fahrenheit or 37.5 degrees Celsius, constitutes a fever in most individuals. Rectal temperatures over 100.4 F. or 38.0 degrees Celsius, also indicate a fever, particularly in infants under 3 months of age. A low-grade fever is usually thought of as an oral temperature that is less than 101 degrees Fahrenheit, or 38.3 degrees Celsius. A moderate-grade fever is an oral temperature in the 102 to 103 degree Fahrenheit range (38.8 to 39.4 degrees Celsius). Temperatures over 104 F. or 40 Celsius are considered high grade, but alone (no other symptoms) are not harmful. Temperatures over 106 F. can be harmful to an individual, particularly if prolonged.