From the standpoint of statistics, both centigrade and Fahrenheit are called interval scale measurements. There’s no meaningful zero point, and thus it’s incorrect to say that any temperature is “twice as hot” or “three times as cold” as another. For such statements to mean anything, you’d have to be using Kelvin (which is ratio scale).
In any kind of scientific context, yes. But that’s as much to do with the meaninglessness of the terms ‘hot’ and ‘cold’ as it is the ‘twice as’ bit.
In plenty of other contexts, and properly qualified, it can be perfectly meaningful.
It’s a bit like me saying “Paris is twice as far away as Bristol”. It’s meaningless, possibly incorrect, unless the reader understands that I’m starting in Bognor Regis, and measuring as the crow flies. But if you DO know that (or if I state it), “Paris is twice as far away as Bristol” is correct and meaningful.
Brits do the same thing.
Distance in miles, although smaller measurements in cm (mostly).
Personal weight in stones and pounds.
Produce weight in kilos (unless you’re old).
Temperature (mostly) in Celsius.
Beer in pints, other liquids generally in litres.
All over the shop, it is.
Well, we Americans do buy soda water in two liter increments.
For what it’s worth, to me Celsius is as natural as you can get, while Fahrenheit is just plain weird. 
If the Fahrenheit scale were objectively superior, wouldn’t countries the world over be switching to it?
Similar issues in India. In fact, I don’t know if there’s anybody playing with as many units and number systems as Indians.
Distance in km, but many smaller units, including personal height, in feet and inches
House areas typically measured in square yards
Atmospheric Temperature in Celsius
Body temperatures in Fahrenheit - So I can compute 45 degrees = hot day, and 102 = fever, but won’t be able to tell you if 100 means a hot or cold day
Beer also in pints
All other liquid measurements in litres
Produce weight in Indian units - pao, which I believe has now come to mean quarter kilo, although it didn’t always
Number systems - we have lakhs and crores, instead of millions and billions. 1 lakh = 100 thousand, 1 crore = 100 lakhs
Of course, since the rest of the world uses millions and billions, we ALSO have those.
Perhaps the only unit we don’t use is miles, or gallons. Thank Og for small mercies.
During my 11 years in Canada, I never quite got used to thinking in Celcius, so I had a mnemonic to help me remember, as some of the temperatures relate to each other in some memorable way. So I can remember that 16C is 61F, 28C is 82F, and 20C is 70F. I’m not certain if those are precise or approximate relations, but it worked to give me a ballpark for figuring out how warm or cool it was. Freezing at 0C is easy enough, I liked the convenience of that.
I got into the habit of following the kilometers per hour speed limits on the signs, but never quite got a feeling for what the corresponding speed in MPH would be, even though they were right there together on the speedometer. When I gave my car to my daughter in the States, she had to be careful to look at the inner dial with the MPH instead of the outer one with the KPH.
That would, in fact, get us closer to the original Celcius scale, where water froze at 100 and boiled at 0. Cite
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Whereas the UK uses an intutitive system: ‘m’ relating to distance could mean in miles or meters; human height is normally measured in feet and inches, but any medical charts are in centimeters; human weight is normally in stones, which aren’t commonly used for anything else; beer is sold as a pint in a pub, 500ml in a shop; temperature is probably in celcius, unless you’re talking to someone over 50ish, in which case it’s a 50-50 shot at farenheit and best of all, a billion could mean 1000,000,000 or 1000,000,000,000, which is a pretty big margin of error.
It’s a perfectly sensible system, I don’t know why more places don’t adopt it.
I’ve pretty much just tried to stop using the word billion. “Thousand million” or “Million million”. Much less chance of a screw up that way.
British people of my age (mid 30s) are pretty mixed-up (or should I say polyglot) in terms of units.
In temperature terms, when it’s warm I think in Fahrenheit (over 70 is getting into pleasant territory, over 80 is pretty warm, over 90 is hot, and over 100 you’re not in England any more!) but when it’s cold I think in Celsius (it’ll get down to minus 5 tonight; it barely got above zero today, etc.) I think most people of my age think more exclusively in Celsius though, the Fahrenheit thing may be my parents’ influence. For cooking I think in Celsius, but to be honest I only usually use the oven at one of three temperatures: 230C or so is hot, for pizzas and suchlike, 180C is what pretty much everything else needs, and 140C is low.
Road distances are in miles, but heights of hills etc are in metres (because that’s what’s on the maps). Ordnance Survey maps do have 1km grid squares, but if I use those to eyeball a distance I’ll still convert it to miles in my head. People’s heights are always in feet and inches.
Similarly people’s weights are in stones and pounds, or pounds and ounces for babies, and dieters lose X pounds, but if I’m cooking I’ll weigh stuff out in grams, or measure out millilitres for liquids. I do actually now have a set of “cup” measures, but that’s only if I want to follow American recipes I’ve got from the internet. Using volume measurements for dry goods just seems very wrong.
A US billion is 10[sup]9[/sup], while a proper, non-Anglo Euro billion is 10[sup]12[/sup]. I guess you guys just can’t decide whether you’re predominantly Euro or predominantly Anglo…
This is why I, like amanset, try to avoid the word “billion”. I prefer exponential notation for anything bigger than a thousand thousands. 
Speaking of Km vs Miles
Because I often tour in Canada and some in Europe, Km is pretty easy basically 1km is .6mi. The cool thing I have figured out is this, if you leave the gps in km it seems like you are traveling faster because the units roll over faster. I figured this out driving back from Toronto to Newark NJ
Just a psychological trick but it works
Capt
Also, if you stand further away from things, they look smaller. You can make even really tall people look tiny with this technique.
That should make things easier - every country makes our own measurement systems. 
And then you can squish their heads.
Talk to just about any Canadian about swimming pool temperatures, and you’ll get your answer in Fahrenheit. Not exactly sure why.
Anyway, there plenty of resolution in Celsius for everyday temperatures.
I grew up in Salt Lake City, then came to Japan once when I was 20, a few times in between and then here since 1990.
My preference for units for walking or biking is Salt Lake City blocks, as that is what I grew up with.
Not only that, there are seven to a mile, which is about 4.4 block per km. See how much more logical that is to have a round number? 
I can relate. You do get used to it. I came back from taking the kids to daycare and thought it was probably 12 deg C. Checking it was 10. Once you can get to within that sort of range, you’re OK.
Even worse, there is a perfectly good word for a thousand million, derivatives of which are used in many European countries.