If your recipe calls for baking your cake at 400 degrees Fahrenheit for a period of 45 minutes, and the oven's temperature dial only reads in Celsius, you are not out of luck. Converting from Fahrenheit to Celsius follows a standard conversion formula that requires only basic math. Converting 400 degrees is therefore quite simple, letting you have your cake and eat it, too.
Subtract 32 from the temperature in Fahrenheit. 400 minus 32 is 368. Subtracting 32 from the given Fahrenheit temperature is always the first step in the conversion to Celsius, and therefore 32 is viewed as a constant.
Multiply 368 by 5. Multiplying 368 by 5 results in 1,840.
Divide 1,840 by 9. 1,840 divided by 9 equals 204.4 degrees Celsius. The process of multiplying by 5 and then dividing by 9 represents the fraction 5/9. This fraction is another constant in the conversion of the temperature.