It works like this...
Tc = (5/9)*(Tf-32)
where Tc = temperature in degrees Celsius, Tf = temperature in degrees Fahrenheit
For example, suppose you have a Fahrenheit temperature of 98.6 degrees and you wanted to convert it into degrees Celsius. Using the above formula, you would first subtract 32 from the Fahrenheit temperature and get 66.6. Then you multiply 66.6 by five-ninths and get 37 degrees Celsius.
The formula to convert a Celsius temperature into degrees Fahrenheit is:
Tf = (9/5)*Tc+32
For example, suppose you have a Celsius temperature of 100 degrees and you want to convert it into degrees Fahrenheit. Using the above formula, you first multiply the Celsius temperature reading by nine-fifths and get 180. Then you add 32 to 180 and get 212 degrees Fahrenheit.
The point at which Celsius and Fahrenheit are the same temperature is -40, that is 40 below zero.