Double the number, then reduce by one-tenth the doubled number, then add 32
Example: To convert 25 C double it to 50, reduce by 5 to get 45, then add 32 to get 77 F.
The reason this works is because 9/5 = 10/5 - 1/5. And the nice thing about this is that it is an exact conversion not an estimation.
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“Easy”
Ok maybe a bit of a stretch, but definitely easier than directly calculating 9/5ths.
9/5 is easy though, you double then subtract a tenth
Why would I want to convert TO Fahrenheit? =/
every 10 degrees Celcius is 18 Fahrenheit.
0c is 32
10 c is 32 + 18 or 50f
20c is 50 + 18 or 68f
30c is 68 + 18 or 86f
40c is 86 + 18 or 104f
Congrats you can now dress comfortably when you travel.
It’s even easier to skip the “reduce by 1/10” step and you still get close. It gets less and less accurate the larger the number becomes, but most people are doing this for day-to-day outdoor temps and it’s more than good enough for that to get close. Maybe don’t rely on it for baking, though.
edited to add, also instead of “adding 32” it’s often easier to think about just adding 30.
Is searching for “25 C in F” considered cheating?
That’s neat but I definitely won’t remember
If you do not need this often, it is hard to remember. I work with many foreign countries, so I need this often.
Just double it
I rarely care about the actual number. “Cold”, “Not bad”, “Warm”, and “Hot” cover 99% of my weather related temperature interactions. I have also memorized 3 easy conversion points to estimate from if I care. If I really care…well I don’t think that I ever have. Maybe cooking instructions, then I might care, but even that is usually just by feel. I’m not a baker.
10C = 50F 28C = 82F 40C = 104FI always multiply by 2 and add 30
Good enough for estimating, but not accuracy.
What about negative numbers
Works just the same:
-10 C doubles to -20, reduce by -2 to -18, and add 32 to get 14 F.
I think I was getting confused with the “reducing” a negative number. But yeah reducing a negative negatively moves it positively
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