My Celsius-Fahrenheit trick

2025-05-28

I'll share my mental shortcut for converting between Celsius and Fahrenheit temperature scales, based on a handy observation:

1 °C ≈ 34 ° F

One equals thirty-four. Each 1 degree above/below freezing in Celsius is about 2 degrees above/below freezing in Fahrenheit.

This is roughly accurate for human-scale weather temperatures. This trick tends to be off from the actual conversion by a few degrees, but it's good enough to save the effort of having to look it up.

Let's practice!

How much is 26 °C in degrees Fahrenheit?

That's 26 degrees above freezing in Celsius, so it's double that much above freezing in Fahrenheit. Double 26 is 52, so my estimate says it's 52 degrees above freezing. That's 52 + 32 = 84 °F.

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The actual answer is 78.8 °F. The estimate was about 5 °F or 2.5 °C off.

The TV said it was going to be 1 °F in Chicago today. What is that in Celsius?

That's 31 degrees below freezing in Fahrenheit. It's half that much below freezing in Celsius. Half of 31 is 15.5, and 15.5 degrees below freezing in Celsius is -15.5 °C.

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The actual answer is -17.2 °C. Again, only a few degrees off.

Okay, typing out the explanation of my trick makes it look convoluted. But, hey, it works for me and my brain. One step along one number line is two steps on a different number line.

"Frozen water is 32% hot"

That "hot percentage" mnemonic is good enough for an intuition of typical weather temperatures in Fahrenheit, though it does imply some strange ideas of temperature. Thankfully, no one is doing science with vague estimations like these, so nitpicking is pointless. Ultimately, how we scale units to be useful to us has always been completely arbitrary.

Yakutsk

Fun fact: Yakutsk, Russia is the largest city with year-round permafrost. -40° is normal in the winter! They still manage to have 30 °C summers.

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