I would hope that the easiest reference to give would be this one 
On the Fahrenheit scale, why is 32 freezing and 212 boiling? What do 0 and 100 mean? (A Straight Dope Classic from Cecil’s Storehouse of Human Knowledge)
If you want to be really cool, of course you will use the Réaumur scale,in which the freezing and boiling points of water are set to 0 and 80 degrees respectively.
[°C] = [°Ré] × 5⁄4
[°Ré] = [°C] × 4⁄5
Or
[°F] = [°Ré] × 9⁄4 + 32
[°Ré] = ([°F] − 32) × 4⁄9
…It keeps them fresh and crisp!
To pick a nit, things tend to get mushy and gross after they’ve been at -40. If kept at -40, they’ll be pretty hard. Maybe Sweden is mushy and gross - I don’t know, never having been there.
Don’t bother with conversions at all – just remember a few common temps, and you can think in Celsius:
180°C = oven baking temp
100°C = boiling water
37°C = normal body temp
20°C = comfortable room temp
0°C = freezing water
-40°C = -40°F = cold as hell in either scale!
Coincidentally, the fact that it is due to be +40 C in some parts of Australia next week is also one of the reasons why we drink.
Some drink to keep warm, some drink to keep cool.
And some drink just because.
Moving thread from IMHO to MPSIMS.
Or the rhyme to the effect of “thirty is hot, twenty is nice, ten is cold, zero is ice”.
Or, you can, you know, have your country adopt a friggin’ system that makes sense and everyone else understands!!!
I mean, why, when 200 countries use metric, and 3 use the Imperial system (US, Liberia, and Myanmar) do the rest of us have to cater to your whims? Gah!
I say the 200 of us could take you in a fight, we should try to make your heads aslode by referencing everything in strange measurements …
104 F?! Christ, I hope it’s a dry heat.
I know! Seriously, get on board with the rest of the world. Then I can take down the F/C chart I have beside my desk so I don’t have to look up fahrenheit temperatures constantly when we discuss weather stuff on the board (“It’s only 20 degrees today!” So what? What is that in celsius? Oh, -7 - that is cold for a southern city.)
ETA: This problem should be taken care of once we have a world government. Buh-bye, imperial measurements! We hardly knew ye.
-40 without wind is great weather for a walk. At that temperature, it’s usually sunny outside, great for the morale. The snow becomes sort of brittle and it makes a sort of a crystalline sound underfoot. I love it.
I go up to Canada (Toronto area) quite a bit. It seems they only use centigrade for measuring outside temps. They still use Fahrenheit for measuring body temperature and indoor temps. Also, they use the metric system for driving distances, but still use feet and inches for measuring height and pounds for measuring weight. Both my kids were born in Canada and both of their birth release forms have their height in inches and weight in pounds.
So…at least we’re consistent! 
Huh. I always thought that was the funny thing about Celsius.
No, just way the hell up North 'round the Arctic Circle. Down here in Stockholm it’s been about -10 C (14 F) the last couple of days, still pretty bitter but not -40 cold.
Since I started living here I’ve been practicing converting Celsius to Fahrenheit in my head and I’ve gotten pretty good at it. Fun math geekery!
The funny thing about the Celsius scale is it was originally designed backwards. For some inexplicable reason (at least no reason I ever heard) it was designed with 0 being the boiling point of water and 100 being the freezing point.
At some point someone thankfully made the smart decision to flip it around.
I know Jamaica and Belize do, so that’s five right there.
If you’re in the US and the sun is setting at 3, then you gotta be in some place like Fairbanks (setting at 3:11, but the day length is growing by nearly 5 minutes a day right now).
The fact that -40 C = -40 F gives a neat conversion method. Namely, add 40, multiply by 5/9 (to go F --> C) or 9/5 (C --> F) and then subtract 40. E.g., for 20C this gets you 9/5*60 - 40 = 108 - 60 = 68.
Since we switched around 35 years ago, I am sort of comfortable with C for air temp. But I still express body temp in F and so does my doctor.
I don’t know about Belize, but according to this site, the conversion of Jamaica to the metric system is well under way.
It’s messy. I wish we’d finish converting to metric. I never thought that after the conservatives pulled the plug on the process, we’d languish in this unpleasant between state for a generation! On the other hand, we grew up sort of trilingual: we can understand the basics of Imperial, US and metric.
And I’ll add my standard disclaimer: the Imperial system is not the US Customary System of Units! The gallons and related units differ. (1 Imperial gallon = 4.5 L; 1 US gallon = 3.8 L.)