-40° Celsius is actually equal to -40° Fahrenheit, it's the temperature at which the two meet. 0° Fahrenheit is about -18° Celsius, did you perhaps multiply 0 b

-40° Celsius is actually equal to -40° Fahrenheit, it's the temperature at which the two meet. 0° Fahrenheit is about -18° Celsius, did you perhaps multiply 0 by 5/9 then subtract 32 instead of the other way around?