The Easy Way to Convert between Celsius and Fahrenheit
Converting between temperatures on the Celsius and Fahrenheit scales is easy. I've been doing it in my head for over a decade now. Yeah, I know I'm a weirdo, using the metric system here in the US when no one else does. But if you've been reading this blog for a while, you already knew I was odd, especially if you've also read my bio over at Green Building Advisor.
Anyway, it's helpful to be able to convert between Celsius and Fahrenheit if you go to other some other countries...Well, OK, it's pretty much all other countries. You could, of course, install an app on your phone that would do the conversion for you, but where's the fun in that?!
Imagine that you woke up today in Atlanta, and all the news outlets were suddenly talking only in Celsius temperatures. Their forecast for the whole upcoming weekend, Friday through Sunday, is for a high temperature of 39° C.
Is that really hot? Is it going to be a gorgeous weekend? Should you make sure your furnace is working? Buy ice?
You could try to remember that equation you learned in school. Let's see, do I add 32 and then multiply by 1.8? Do I divide by 1.8 and subtract 32? What order do I do that in, and which one is which? Where's my calculator?!
That's the hard way, my friend! The easy way is to learn the principles in the table below.

Notice the two lines highlighted in yellow. Those are my two main reference points. I can figure out any temperature I want by skipping along in 5° C increments, each time adding or subtracting 9° F. When a temperature is between the numbers in the table, then I look at which line it's closest to and add or subtract multiples of 1.8° F for each degree C.
It's really not that hard. And yes, 39° C really is the forecast for Atlanta this weekend. You should be able to figure out from the table above that that is going to have us living up to our silly nickname: Hotlanta!
Photo of Celsius Summer Ale by walknboston from flickr.com, used under a Creative Commons license.