Or is it just more familiar? We all like what we're accustomed to. Is there some reason Celsius 'makes sense'? Why does it make sense that 22 is comfortable but 40 is miserably hot? It doesn't make any more sense than 72 and 100.

The familiar part has changed for Canadians.

I grew up during the transition period I was too young to know Fahrenheit, I had just entered school when the switch was occurring.

My parents are pretty well used to Celsius now but still may occasionally use Fahrenheit such as some electronic device that allows F or C they choose F.

It's still a but messed up though since Canada borders the US. The old joke being weather reports that show the border with the US say Detroit shown as 90 and Windsor as 32 "See Marge as soon as you cross the border into Canada it goes dow to 32!"

But still you get people of all ages saying things like "300km/h wow that's nearly 200 mph" or "You weigh 70kg what's that like 150 pounds?". It's more due to history and the influence of the US on our culture, I bet more french speaking areas like Quebec, northern NB don't do that but who knows maybe they do.

I was born and raised in Florida. I now live in Sweden. Because of experience, I understand C pretty well between -15 and +10, and between +80 and +100 (Swedish sauna temperatures).

Between +20 and +50 I'm still more comfortable with 70F-120F. I also spent some time in Illinois, where I learned to understand the subzero range from -15F to 0F.

At LOX temperatures of 90K and below, I'm most comfortable in Kelvin. ;)

0°C - water turns into ice 100°C - water boils and turns into steam

-30°C and below - very cold weather +30°C and above - very hot weather

But the freeze/boil numbers are arbitrary as well only being true at sea-level. Where I live in Colorado, we're 1 mile (cough, 1.6 km) above sea level meaning those formulas are meaningless.

They aren't meaningless. Water boils at 95 C at your altitude - effectively the same temperature for all "common" usages. E.g. you'd still better not stick your hand into boiling water.

A <5% error for the zone that >99% of humans inhabit seems pretty practical to me. The freezing point is effectively identical.

iirc, water boils at 95C is around 5000m altitude, no one lives normally there - even La Paz is less than 4000.

Well its rather easy to make your own thermometer using the Celsius scale. Put quicksilver in a small glass tube and put it outside. When water starts to freeze mark the current position with 0. Drop it in boiling water and mark it with 100. Evenly distribute now 98 markings between the two existing ones and voila you have just made your own thermometer :)

Evenly distributing 98 markings is hard. Evenly distributing 64 is easy -- just halve the range six times. That's why the distance from freezing water to body temperature is 64 Fahrenheit degrees.

Except...

Freezing point of water: 32°F Average human body temperature (oral): 98.2°F

So that's 66.2°F, not 64°F.

Those two temperatures were the original reference points for the Fahrenheit scale, and body temperature was defined as 96°.

The current definition is relative to the melting point of ice (32°F), and the boiling point of water at standard atmospheric pressure (212°F, which is exactly 180°F higher than the freezing point). Except now body temperature is 98.2°F instead of 96°.

If you want a thermometer calibrated in Fahrenheit, you have exactly the same problem as you do with Celsius. You just have to put 178 markings between the two reference points, rather than 98.

I don't think its advisable to use my self-made quicksilver thermometer for any kind of body temperature measurement.

Which makes no difference because you're eyeballing it to start with. You can just as easily divide the 0-100 range in half a bunch of times. Your thermometer is not achieving <1 degree accuracy.

Of course if you have a tool to accurately measure halves, then you can also measure any other division you care to use.

All depends what you are used to - I would say 15C or so is "comfortably warm", 22C is definitely "warm" and 40C is utterly miserable with no wind but really nice with a breeze and in the shade....

People generally start sunbathing, wearing T-shirts and flip-flops, when the temperature goes above 10C here...

Could you say a bit more about why you feel it makes sense, perhaps with a chart like the one I wrote up?

I'll bite (and I grew up in one of the colder parts of Canada, so I'd call 0F a cold but not unreasonable winter day).

-30: Avoid going outside, if you do don't leave any exposed skin

-20: A cold winter day: toque, scarf, mittens, winter coat and boots are must have

-10: An average winter day: same load-out as above, but you'll be more comfortable

0: A mild winter day: snow possible, you may leave your winter jacket open, or skip the scarf

10: Early spring or late fall: you might be able to get away with a light jacket, but I'd leave that until 15

15: Long pants and light jacket

20: Leave the jacket home, maybe wear shorts or a t-shirt

25: Comfortable summer weather: shorts and t-shirt

30: Annoyingly hot summer weather, good for swimming

35 or higher: hole up somewhere with AC

LOL. I'm in Western Australia:

<10: Bloody cold, avoid going outside if possible. Rug up if you do.

15: Winter. Probably rain and wind.

20: Cool Autumn / Spring, you might need a jumper outside.

25: Vaguely warmish, t-shirt weather.

30: Getting warm, wear shorts and t-shirt.

35: Beach weather, avoid going outside for too long if you're in office attire and don't want sweat patches.

40+: Hot beach weather, stay out of the sun (or in the water) in the middle of the day.

Interesting...I'm in the UK, for me 24°C with a light breeze makes for a perfect Summer's day: warm enough to walk around without sweating buckets. 30°C is uncomfortably hot. I guess it's all relative to what you're used to (and what you're doing e.g. day at the beach or walking in the city).

Well, people don't for the most part look forward to 40 degree days - this is warmer than body temperature, so you have to engage in some form of cooling. Going to the beach is one form of cooling :) Avoid being outside, drink lots of fluids, AC if you can, anything, really. Construction workers generally stop work around 36, from memory. Conversely, people here will tell stories about the crazy British neighbour who is out doing the gardening in a singlet when it's only 10 degrees.

Here in Melbourne we'll have several 40-degree days each summer, and the only large city with more that I'm aware of is Phoenix. There are heaps of large cities that are warmer in general, but they don't peak quite as high. Record is 46.2, set a few years ago. Not a pleasant day, especially since it was after a few similar days...

Victoria, Australia here. About the same, except we can get three or four of those all in the one day. (The running joke is that if you don’t like the weather in Melbourne, wait.)

I’ve lived in both the low and highlands of Papua New Guinea and they have two types of weather: dry and wet. In the lowlands you do not go outside without wearing a hat as the sun will actively try and kill you. When a PNG friend visited us in Melbourne, it was a 30°C day, we were in shorts and t-shirts, he was in jeans and wearing a parka to keep warm.

Canadian here as well I see some people in shorts at 10C maybe even at 0C mostly "dudes" in their 20s and late teens. I even see bigger (fatter) guys in shorts in the middle of winter now it seems to be a thing.

After a cold winter 0C even -10C feels warm especially if there isn't any wind.

I don't know anyone who zips up their jacket unless it's -15C or -10C and windy.

It's the wind that gets you, -20C is nothing if there isn't any wind.

But really it also depends a lot on perspective since 10C in the spring feels very warm but 10C in the fall feels very cold. Maybe a lot of the descriptions depend on year round average temperatures, I can image people in southern California with a smaller temperature range would not feel as much of a difference as a Canadian would.

Not bad.

As a Brit:

-20: Inside a food freezer.

-10: Ski trousers weather. Doesn't happen where I live.

-5: There'll be snow, or at least frost. Hat & gloves weather. Happens one or two days a year.

0: Freezing, usefully. Full-length coat.

5: Pretty cold - not unusual for a winter day. Fridge temperature. Don't forget your jacket.

10: A warmer winter day, or typical early spring.

15: Spring/Autumn; temperature where I'd stop bothering with a jacket.

20: "room temperature" for science (though many actual rooms are a degree or two higher than this). Comfortable.

25: A sunny summer's day. Pleasantly warm.

30: Starting to get towards uncomfortably hot. Notwithstanding this year, I'd only expect a few days this warm in a year.

35: Doesn't happen where I live. You want to be in the pool or somewhere with AC when it's this hot.

40: On a person, serious fever.

60-70: Nice for a sauna. Warm drink (e.g. tea)

That's pretty much it, except 90C sauna is quite decent.