Fahrenheit vs. Celsius vs. Kelvin

Fun fact time, -40F is -40C.

And 575F is 575K

Fahrenheit is a strange scale.
- It's just designed with a slightly different set of assumptions.
  
  Instead of water freezing and boiling 100° apart, it's 180° in fahrenheit. That makes it so that they're on the opposite sides of a temperature gauge, and a degree of rotation of the gauge matches a degree of temperature.
  Instead of zero being the freezing point of water under specific conditions, it's a brine solution whose temperature will stabilize in a way that's useful for using as a calibration point.
  
  Stripped of its context, it's odd. But it's not irrational, just no longer consensus as the standard, and as such deprecated.
- Fahrenheit makes sense for humans. Most of your day to day climates are in the 0 to 100 scale, and every 10 degrees is a noticeable level change.
  
  100 super hot day, approaching unsafe without counter measures
  
  90 really hot day, slightly annoying and should take precautions
  
  80, hot day, more annoying than anything
  
  70, beautiful day, enjoy it
  
  60 not to bad, if it's windy you could be slightly on the cold side
  
  50 long sleeves or maybe a hoodie
  
  40 definitely a jacket, and hat
  
  30 full on coat, scarfe, and hat
  
  20 multiple layers of out for a while, maybe double pants
  
  10 annoyingly cold, need to start thinking about the safety precautions
  
  0 and below, temperature now measured in hold long you can be outside before danger
  
  Celsius makes sense for science stuff because it's derived from science stuff, so things like calories and energy work with it. But it doesn't really apply to everyday life as well. So it actually makes sense to use both units for the things the are good at.
And at what temperatures are C and K equal?
- Never. They use the same spacing between degrees. The Kelvin scale was derived from the Celsius scale, just placing the 0° at absolute zero rather than at the freezing point of water.

Fahrenheit: how hot humans feel

Celsius: how hot water feels

Kelvin & Rankine: how hot atoms feel

I don’t think how hot humans feel works at all, it’s just arbitrary

Can humans survive 100 degree heat? Yes so it doesn’t represent 100%

150 for 3rd degree burns (almost instant), does Fahrenheit go off base 150? Also no

What about cold? Well -40 requires a lot of layers, so then +40 should be pretty hot for humans right? Nope, because it’s not related to humans at all
- 100°F was supposed to be average human body temp. Guy who made the scale fucked up his math and we ended up actually at 98.6°F
- If farenheit represents how humans feel then 50 is the most comfortable temperature right?
- Neither will kill you (usually) but both suck.
- I don’t think how hot humans feel works at all, it’s just arbitrary
  
  Fahrenheit was originally calculated to be 64 even divisions between water freezing temp and human body temp, then 32 more units below freezing.
  
  Then ambient human body temp was recalculated from 96F to 98.6F.
  
  So it's not exactly arbitrary. It's based on powers of 2, based upon an inaccurate measurement.
- Can humans survive 100 degree heat? Yes so it doesn’t represent 100%
  
  I have no idea what this means.
  
  150 for 3rd degree burns (almost instant), does Fahrenheit go off base 150? Also no
  
  What about cold? Well -40 requires a lot of layers, so then +40 should be pretty hot for humans right? Nope, because it’s not related to humans at all
  
  Why do these matter? What percentage of humans live where it's regularly -40 degrees? Why does the scale need to be perfect in your opinion? And how is Celsius better?
- No one said it represents "100%", whatever that is even supposed to mean. 100F is really hot outside. 0 F is really cold. Doesn't have to make 100% sense. Celsius doesn't make perfect sense either. There is no perfect magical scale that works completely.
Yeah, this gets repeated (by Americans) every time a discussion about temperature measuring systems comes up, but it is complete nonsense. The vast majority of Earth's population are completely fine with measuring how hot they feel in celsius, it is only people who are unaccustomed to that system who thinks it is somehow unqualified to do that.
- American who lives in a country that uses C now.
  
  20=frickin cold 30=swampy ass 40=nope
  
  Not enough degrees of separation
- I lived for a third of my life in a country that uses Celsius, and the switch to Fahrenheit was not only seamless, it made much more sense to me intuitively. Whereas I was fine using Celsius, I don't really want to go back.

Based on human perception, based on water chemistry, based on physics.

You'll be shocked to learn that the distance in Kelvin is also adjusted to water "chemistry", albeit changing the aggregate state seems more physics to me, since no molceules are reacting with each other.
- Thankfully that has been redefined using the Boltzmann constant, so now anyone in the universe can agree on °C and K without needing to measure any Vienna standard ocean water.
- You can't change the aggregate state of a single molecule, or how do you mean that? Excluding plasma.
Zero Fahrenheit is the freezing point of brine (of a certain concentration). That's water chemistry.

Originally, 90F was based on the average human body temperature, but that later changed to 96F, which just goes to show how arbitrary that scale is.
- It's all arbitrary. Someone just decided to base a scale off of something and that something isn't fixed from the start. The meter used to be based off the measurement of the earth, but now it's based off of light.
  
  It's just some random semi-useful starting point that we all agree on so we're using the same language.
So, Kelvin in Physics, Celsius in daily usage and Fahrenheit...?

Since when is 0°C "fairly cold" it's literally freezing.

0°C is completely fine with jeans and a thick jacket, especially when it's sunny and there isn't much wind. It's cold, but there's probably not much ice or snow, if anything, probably mostly slush.

Compared to say -20 C where you should have a good ski jacket and ski pants, warm shoes and socks, generally multiple layers everywhere, winter gloves and so on.
- It can be -20 C and you can be still fine with jeans and a jacket if it isn't windy.
  
  What I'm saying is temperature alone doesn't tell you the whole story.
- But so is 100°F completely fine with a shirt and shorts and some shade.
  
  So basically: |0°F| > |100°F|, where | is the mathematical absolute operator.
  
  0°F is really cold, while 100°F is merely somewhat hot.
- https://www.brennanshvac.com/article/humidity-temperature-strange-link-know#:~:text=In cold weather%2C high humidity,of warm air around you.
- Humidity. I'm guessing you don't live in a humid place because freezing temps are horrifically cold here. You will need a winter coat and multiple layers of your going to be outside for a while. I layer long Johns under my pants and wear my parka and a light jacket as well as 2 layers of socks. Everytime a northerner comes here they are shocked at the cold/heat. That's because the air here is full of water to the point that you will actually get wet just from the humidity, not even sweating.
It is also literally melting.
I've been in -37C snow shoveling. Since then 0C doesn't even register as cold to me
- Yep, and I've been in 110C in sauna. It's pretty fucking hot but not death
The northern half of the US laughs
The temperature that water freezes at is only fairly cold weather by a lot of people's perception.
I'd call it "chilly". No jacket for running to the mailbox, or if I'll be outside for half an hour or so. Light jacket otherwise. I don't expect it to snow, since it's not actually cold enough usually, and there won't be ice on the ground unless it's just warmed up.

So it might be "freezing", but that doesn't make it cold.
- It's almost like being 'fairly cold for humans' is a wide range, and subjective, therefore useless as a baseline.
- In Aus we say it's fucking freezing
Many places in the US, particularly in the East and Midwest, experience average temperatures at or below freezing (32°F) in the winter, so while it's definitely cold, it's often not considered really cold. It's not until you move further towards 0 and the negatives that most people in that area feel really cold (like weather advisory levels). Of course the further north you go, the more normal those temps are. Likewise, it's definitely not unheard of for temps to hit 100°F (37°C) in the Southwest, but it would be considered pretty hot for much of the country, and even Texas suffers at sustained temps like that.
- Freezing temps here are definitely considered very cold. Cold enough that you need multiple layers and you should be wrapping your pipes to prevent freezing. It's very humid here. Our freezing is insanely cold. Like chills you to your bones cold. Our hot here is insanely hot as well.
I would put it at a 3/10
We're not made out of water.
- You're failing at pretending to be human. We're literally made of water. About 80% of us is water.

I'd like to propose a discussion between a person from Arizona and a person from Alaska to define what is "Really hot outside"

Im from Texas, and 100F is "stay inside in the AC" weather. I bet an Arizonan would say the same.
- Being from a particularly hot or cold location doesn't make you immune to heat or cold, it makes you a connoisseur of heat and cold. You get better at recognizing gradations of extreme temperature (knowing which are uncomfortable and which can literally kill you if you're not careful), you learn how to plan ahead and dress for the weather, and you develop emotional coping systems for extremes.
  
  But if it's either 100°F or 0°F, no matter where you're from, that's a temperature to be wary of.
- Heyo! I’m from Arizona. 100 is not “stay inside the AC” weather for us, it’s practically “time to get a light jacket” weather.
Or cold

Celcius is the logical choice. The others are just crazy.

Kelvin and Celsius are the same, just offset onto absolute zero or the water freezing point
- Yeah, often it is just way more convenient to use the Kelvin scale without any negative temperatures for some calculations and formulas then Celsius
Because aligning to the temperature at which water boils is the objectively correct choice?

"Hey, how hot is it going to be today?"

"Well water is about 1/3rd the way to boiling, so about 30 degrees"
- True, we should be using a temperature scale that was defined on how cold it was in Gdańsk, Poland in the winter of 1708, something the average man is more familiar with than water temperature, right?
- When it's "freezing cold" or "ice cold" outside, what do you think is freezing? When something is "boiling hot", what is boiling exactly?
  
  We use water to describe temperature even without using Celsius, because it's everywhere around us, and we are literally made of this stuff. It's also one of the only materials that goes through three different states in our usual temperature range, so using those as a reference point to measure temperature makes perfect sense imo.
- We used water to decide a lot of measurements. 1ml of water is = 1 gram. A gram of water is also equal to 1 cm^3. It's a beautiful system in that way. Water surrounds us and gives us life, it has chemically interesting properties that make this planet function. Why shouldn't we just base everything off of this one substance?
- The fact that 99.5% of the global population uses it makes it the objectively correct choice.
  
  The remaining .5% can keep bashing their heads against a wall if they like though
- Maybe ecause everyone uses it? Just so you know nobody even knows how fahrenhiet was defined first, everyone in the scientific community uses kelvin which is celsius but shifted so absolute zero is zero on it and the us actually uses si they just convert it to imperial so conversion between them is easier. There is point to imperial units other than its hard to switch between systems.
- You can get used to any scale
- The temperature of water is very intuitive in nature. Dip ur hand in ice water. That's almost 0C. Dip ur finger in boiling water (very quickly). That's 100C. Dip ur finger in coffee whose temperature is fit for consumption: that's around 75-80C. Ur hot water shower is likely between 37 and 41C..
  
  Everything is tied quite well to water. Now compare that to F. What's 0F? What's 100F?
  
  Forget the intuitiveness of celsius. It's also much easier to calculate using celsius. When I say "My coffee was worth 80 calories", I'm referring to a measure called "KCal", which is the amount of energy required to raise the temperature of 1 litre, or 1 Kg of water by 1C. So if u ate something worth 100Kcal, you consumed enough energy to heat 1L/1Kg of water from 0C (ice) to 100C (steam). The average human requires around 2500 KCal everyday. Which is equivalent to 2.5 liters of water. Pretty cool, huh....
  
  Just a quick sidenote: KCal is still not an "SI" unit. "Joules" are what we use here, but that's another story.
- the Celsius nerds are mad at you, I guess. I love it when you see someone make a good point and the downvotes just pile on.
  
  never change, reddit.
  
  edit: they're here! lol. hey guys! have fun with your storming the castle to defeat the evil Fahrenheit! make sure to prepare your spells, you don't wanna get caught out when the negative values come out. 💕

We should really normalise the Japanese system - it makes as much sense as the European system and has the benefit of being "alphabetically" sortable.
- I'm entirely for it.
  
  Handwritten, I often use the military style 09 Oct 2023 just because the meaning is inarguable, but for files and such, it's always YYYY-MM-DD.
  
  I'd also like to see us adopt GMT, just calling noon and midnight whatever number they happen to be in our location. With remote work and jet travel, it makes sense.
  
  And base-12 arithmetic, but that's just a pipe dream.
- Especially true if you include time as well:
  
  Year > Month > Day > Hour > Minute
  
  Vs
  
  Day < Month < Year > Hour > Minute
- Plus it's self-describing! As long as you can read Kanji...
ISO-8601 or bust.

No other format really matters.