I saw this recently on Lifehacker – How to Convert Celsius to Fahrenheit Without Doing Any Math: https://lifehacker.com/how-to-convert-celsius-to-fahrenheit-without-doing-any-1848777530. Longer article.
By Beth Skwarecki April 11, 2022
Will you know the exact temperature? Maybe not. But you’ll know whether to bring a jacket.
I consider myself pretty conversant in metric units. I know that 20 kilograms is 44 pounds (double it and add 10%) and that 5 kilometers is 3 miles (I’ve, uh, run a lot of 5Ks). But celsius temperatures have always been a bit of a mystery to me—until now.
Not only are Celsius and Fahrenheit degrees different sizes (each Celsius degree covers more of the scale) they have different baselines. Zero degrees Fahrenheit is a bitterly cold day in the dead of winter. Zero degrees Celsius means that you’re right on the cusp of where a predicted snow flurry might turn out to be a rain shower, or vice versa.
Because of these two factors, converting is traditionally a two-step process: you need to multiply and add (or subtract and divide). That was still the case last time we covered a way to “quickly” convert from one system to the other—the quickness in that example coming from the suggestion to use 2 and 30 as the relevant conversion factors, instead of 1.8 and 32.