OK, so this post is a bit of a remnant from some brain activity that I was working through while my relatives from the States were visiting here. The weather stations here obviously do their forecasts in degrees Celsius. When the relatives see the forecasts, inevitably, one of them will ask me “how much is that in Fahrenheit?” All I could do in response is give off some rough number based on some ranges that I have in my mind. For example, I know that 32°F is freezing. I know also know that 80°F is a nice warm day. The rest was kind of a blur. Oh, how “fuzzy logic” of me. Anyway, it took me a while to figure out how to calculate conversions on the fly.
On the Internet I kept on encountering 5/9 or 9/5 as the ratio involved with conversion. I’ve tried keeping track of the fraction mentally but in the end with so many numbers would calculations were often off because of some transposed number, or something. What clicked for me was the realization that instead of nine-fifths, 1.8 was so much of an easier number to handle. Indeed. After that, all I needed was to keep a running total in my head and perform some easy addition/subtraction. All I needed were some key numbers to do some nice conversions:
- Multiples of 1.8 up to 9: 1.8, 3.6, 5.4, 7.2, 9.
- Multiples of 18: 18, 36, 54, (maybe 72).
- Freezing point in Fahrenheit: 32.
OK, so what do you do? Well, let’s take Celsius to Fahrenheit first.
- From the absolute value (disregard positive or negative–calculate using positive), for every 10 degrees Celsius count 18.
- Take the left over unconverted degrees Celsius, and if it’s over 5, count 9 more degrees for those 5.
- For the remainder of unconverted degrees, count 1.8°F per degree and add that to the total. Rounding will simplify things.
- If the temperature is below freezing, subtract the total from 32. If it’s above freezing, add it to 32.
There. Looks kind of ugly, yeah? Well, let’s do an example. Let’s convert 23°C.
So, 20°C is 36°F. And 3°C is 5.4°F, but let’s say 5. The total is 36 + 5 = 41°F. Since it’s above freezing, 32 + 41 = 73. So: 23°C is about 73°F. Nice!
Let’s try -16°C.
10°C is 18°F. 5°C is 9°F. 1°C is 1.8°F, but let’s say 2. The total is 18 + 9 + 2 = 29°F. Since it’s below freezing, 32 – 29 = 3. So: -16°C is about 3°F.
Not so bad once you get the hang of it. How do you go the other way though?
- Subtract 32 from the total Fahrenheit.
- Disregarding whether the result is negative or positive, for every 18°F, count 10. Key numbers: 18, 36, 54, (maybe even 72).
- If the remainder is above 9°F, count 5 for those 9.
- Count out the remainder using multiples of 1.8.
- If the starting number was below 32, the temperature is negative. If it was above, the temperature is positive.
So. Let’s try converting…96°F.
96 – 32 is 64°F. We can convert 54 from that to get 30°C. There’s 10°F left over and we can count 9 of that 10 as 5°C. The one degree left over is close enough to 1.8, so we can kind of count it as 1°C. So, the total is 30 + 5 + 1 = 36°C
What about converting 17°F?
17 – 32 is -15 degrees. We know that 9°F is 5°C. There are 6 degrees of 15 left unaccounted for. 6 is just a bit more than 5.4°F which is 3°C. So, the total is 5 + 3 = 8°C. We know the temperature is below freezing, so we say that 17°F is about -8°C.
I swear, these conversions aren’t that bad. I find it interesting to give the mind some exercise by switch units. Impress friends and family with your mad skills!
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