The US is one of the few countries where the temperature measurements are in Fahrenheit. Elsewhere, Celsius is the norm. Usually, when traveling, I want an approximate mapping. Thankfully, it is linear and easy to memorize.
To convert temperature in ºC to ºF - double and add 30 To convert temperature in ºF to ºC - subtract 30 and half
Both of these are approximations for fast calculation ºCºF0301050207030904010550120
The mapping is slightly inaccurate for ease of memorization.