I consider myself pretty conversant in metric units. I know that 20 kilograms is 44 pounds (double it and add 10%) and that five kilometers is three miles (I’ve, uh, run a lot of 5Ks). But Celsius temperatures have always been a bit of a mystery to me—until now.
Why it’s so annoying to convert between Fahrenheit and Celsius
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.
But there’s a better way; all you need to do is memorize four numbers, and flip them to convert. (Or memorize one of them and know that you can add or subtract 12 to get each of the others.)
How to convert temperatures without math
Here’s the trick:
04 degrees Celsius is 40 degrees Fahrenheit (chilly!)
16 degrees Celsius is 61 degrees Fahrenheit (hoodie weather)
28 degrees Celsius is 82 degrees Fahrenheit (balmy!)
40 degrees Celsius is 104 degrees Fahrenheit (stay inside and crank up the A/C)
For these particular numbers, you’re just reversing the digits: 16 becomes 61, get it? The only weird one is 40, but now that you’ve read it, you get the idea. Four degrees Celsius is 40 Fahrenheit, and 40 Celsius is 104 Fahrenheit.
Now, if you’re on vacation and they tell you it’s going to be 32 today, you know that that’s more than 28 (82 Fahrenheit) but thankfully below 40 Celsius (104 F). It’s tank top and shorts weather.
On the other hand, if it’s going to be 10 degrees Celsius, you know that it will be cooler than 61 Fahrenheit (10 is less than 16), but warmer than 40 (10 is more than 4). Bring a jacket, and you’ll be good.
If you can’t remember numbers at all, here’s a poem
Still too much math? Try memorizing this poem:
30 is hot
20 is nice
10 is chilly
and zero is ice
Those numbers are 86, 68, 50, and 32 degrees Fahrenheit, respectively. And a fun bonus fact, in case you’re ever vacationing in the Arctic: -40 is -40 in both scales.