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

ºCºF
030
1050
2070
3090
40105
50120

The mapping is slightly inaccurate for ease of memorization.