In the USA, temperature is not measured in Celsius, but in Fahrenheit. If you are used to thinking in Celsius, you often don't know what to do with the Fahrenheit number. 

It is not always possible to look up the conversion quickly on the internet. However, there is a simple formula that can be used to quickly convert from Fahrenheit to Celsius and from Celsius to Fahrenheit.

Conversion from Celsius to Fahrenheit

Take the number given in Celsius and multiply it by 2, add 30, subtract 2 and get the corresponding value in Fahrenheit.

In other words: 

2X +30 -2 = Y (X= value in Celsius; Y= value in Fahrenheit)

Conversion from Fahrenheit to Celsius

Take the number given in Fahrenheit and subtract 30, add 2 and divide the result by 2 to get the corresponding value in Celsius.

In other words:

(X -30 +2) /2 = Y (Y= value in Celsius; X= value in Fahrenheit)

Of course, one could shorten the path and directly add or subtract 28 instead of 30-2, but it is easier to calculate with 30 in one's head.

Important: The results are not 100% mathematically accurate, but only give an approximate idea. The exact formula for conversion is: 

Y = 9/5X +32 (Y= Fahrenheit; X = Celsius)

X = 5/9(Y - 32) (Y = Fahrenheit; X = Celsius)