The most common temperature conversion that one wants to do is to convert degrees Celsius to degrees Fahrenheit or vice versa. I hope to explain how to do this conversion in such a way that one need not memorize a formula, even to get the exact answer.
First, it is worthwhile to mention a quick and dirty approximation that almost anyone can do in his or her head. It is not exact, but it is useful, if you are traveling to a country that uses a scale that is different than the one you use to think about ambient temperatures.