I consider myself quite familiar with metric units. I know that 20 kilograms roughly equates to 44 pounds (just double it and add 10%), and five kilometers is roughly equivalent to three miles (probably because I’ve run my fair share of 5K races). However, Celsius temperatures have always puzzled me. That is, until now.
The reason behind the annoyance of converting between Fahrenheit and Celsius is quite simple. These two temperature scales not only have different-sized degrees (each Celsius degree covers more ground), but they also boast different starting points. Zero degrees Fahrenheit signifies an incredibly bitter cold day during the heart of winter. In contrast, zero degrees Celsius hovers on the brink of whether a predicted snowfall might transform into a rainy drizzle or vice versa.

Due to these two distinct factors, the conversion process traditionally involves a two-step procedure: multiplication and addition (or subtraction and division). The same applied when we last discussed a “quick” conversion method, which suggested using 2 and 30 as conversion factors instead of the more complex 1.8 and 32.
However, there exists a simpler method—one that only requires the memorization of four key numbers that can be easily flipped to perform conversions (or just memorize one and know that you can add or subtract 12 to obtain the others).
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So, how do you convert temperatures without getting bogged down by math? Here’s the trick:
- 04 degrees Celsius is equivalent to 40 degrees Fahrenheit (a bit chilly!)
- 16 degrees Celsius translates to 61 degrees Fahrenheit (ideal hoodie weather)
- 28 degrees Celsius corresponds to 82 degrees Fahrenheit (pleasantly balmy!)
- 40 degrees Celsius equals a scorching 104 degrees Fahrenheit (stay indoors and crank up the A/C)
For these specific numbers, you’re essentially reversing the digits. For instance, 16 becomes 61. The only exception is 40, but now that you know this rule, it becomes clear that four degrees Celsius equate to 40 degrees Fahrenheit, and 40 Celsius means a blistering 104 Fahrenheit.
Imagine you’re on vacation and you hear the local forecast predicts a high of 32 degrees Celsius today. Thanks to this method, you quickly realize that it’s hotter than 28 degrees Celsius (82 Fahrenheit) but mercifully cooler than 40 Celsius (104 F). It’s officially tank top and shorts weather!

Conversely, if the forecast calls for 10 degrees Celsius, you’ll deduce that it’s chillier than 16 Fahrenheit (since 10 is less than 16), but warmer than 40 Fahrenheit (as 10 exceeds 4). In this case, you’d wisely pack a jacket and be prepared for varying conditions.
And for those who simply can’t remember numbers at all, here’s a handy poem:
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- “30 is hot,
- 20 is nice,
- 10 is chilly,
- and zero is ice.”
These numbers correspond to 86, 68, 50, and 32 degrees Fahrenheit, respectively. As a fun bonus fact, if you ever find yourself vacationing in the Arctic, you’ll discover that -40 is the same in both Celsius and Fahrenheit scales.