when are celsius and fahrenheit numerically equal
Asked by: Hamid A. Khan. The temperature at which Fahrenheit and Celsius thermometer readings are equal is: - 40 degrees. Well if you look at the conversion formulas for Celsius to Fahrenheit, or that of Fahrenheit to Celsius, you can manipulate it mathematically to answer this question. The conversion formula reads: T(F) = T(C) x 9/5 + 32.