Hot enough for you?

July 19, 2012 • 4:56 am

Chicago, like many places, has been in the throes of a heat wave, with temperatures approaching 100º F in the past three days.  Mercifully, Ceiling Cat sent a cooling rain last night, but it will be back in the 90s this weekend.

Although I work with centigrade (Celsius) temperatures in science, I never have managed to absorb them directly because I was raised on Fahrenheit. The one exception is our standard Drosophila-incubator temperature of 25º, which I know by heart is 77ºF. Otherwise I always have to convert in my head (“Centigrade times nine-fifths plus thirty two, etc).  For those of you in my situation, I’ve provided a handy conversion chart below, including the Kelvin scale as a special bonus:

87 thoughts on “Hot enough for you?

  1. I’ve always felt the same way. I’ve said before that the Kelvin scale is best for scientific or engineering computations and Fahrenheit is best for anything that touches skin, leaving the Celsius and Rankine scales as pretty much useless.

  2. Move out here to the desert where 104 F is 40 C. It doesn’t feel any different, but sounds less painful… 😉

    1. I am wilting just THINKING about that! Have you ever tried to fry an egg on a bit of metal left in the sun?

      1. I don’t live in the desert and it was that hot here last week. And humid.

        I did accidentally touch my black mailbox which had been in the sun all day. Not comfortable.

  3. Fortunately we have almost managed to ditch Fahrenheit in the UK, but for talking to Americans, I just remember a few easy values and interpolate: 0C is 32F, 16C is 61F, 28C is 82F.

      1. I think I recall reading that they used to stop work in the Gulags at -25C; below that when you spit it freezes in the air. Only experienced that once in Oslo I think in 1995.

        1. When we were in Longyearbyen we went on a dog sledding trip. We asked the guide why the dogs were rolling around in the snow and she said “They’re trying to cool off; they don’t like it when it’s warmer than -25.”

        2. I experienced -40 F once in a massive storm that dumped 70″ of snow in 48 hours. Like an idiot I was out driving in it when my car overheated. Though I had a proper mix of water/antifreeze in my radiator, it had turned into a viscous jelly that was too thick to circulate.

          So, I donned my 1960’s era Air Force issue Arctic Flight Line Gear, a hand me down from my father, and began walking home. The first few minutes were not so bad, but I got cold very fast. I was amazed at how quickly the cold cut right through all the layers I had on. An interesting sensation that really is best described by the word “cut”. It was also difficult to see because my eyes were so dry (I assume from the surface moisture freezing) I could not stop blinking and you can’t get a clear image with a dry eyeball.

          Luckily a kind soul with a properly outfitted all wheel drive vehicle was out on a safety patrol and picked me up.

          1. Isn’t the danger sweating under your clothes if you exert yourself in the cold, then the sweat cannot evaporate & you get cold?

            1. That is certainly a danger. The general rule is if you are warm enough take a layer, or layers, off. The goal is to keep sweating down to a minimum by wearing enough to just be comfortable. If you are engaged in physical activity that can get tricky, and become dangerous if there is no sanctuary available.

              The issue is the sweat not being able to get through your clothing and escape, but instead being trapped inside your clothing, changing state to a liquid, and thereby making your clothes wet. Gortex and similar materials are widely used in modern cold weather gear because the pores are of such a size that the material is permeable to water vapor, but not water liquid. This allows the sweat to pass through your clothes and escape to the outside.

              It is tricky to properly design and use cold weather gear that can do that well though. Even with good gear if you don’t wear it properly, or if the combination of temperature and humidity fall outside a certain range, the gear can fail. For example, something as simple as adding an extra layer of material the designers didn’t account for, like your favorite T-shirt, can change things so that a dew point occurs somewhere inside you clothing. The idea is to utilize materials with specific permeability characteristics, arranged in a certain order, so that over a wide range of temperature and humidity ranges water vapor transmission analysis shows no dew points anywhere within the gear.

              1. Thanks for such a full answer! As a ‘sweater’ who doesn’t mind cool & damp but cannot abide warm & damp, I would have to take off layers. Once in Scotland I was in a situation on a mountain in the snow when I was sweating & then the sweat cooled without evaporating so I was cold around my back.

  4. “Centigrade”? A scientist using a non-SI unit name? For shame!

    And if you just need a quick heuristic for most temperatures we humans encounter, “Double it and add 30” is a much easier conversion from Celsius to Fahrenheit than “Centigrade times nine-fifths plus thirty two”.

    And being an American who’s moved to the Great White North, I do prefer Celsius. The anchor points make much more sense that Fahrenheit, and the individual degree differences are more detectable (i.e., a difference between 24C and 25C is much more noticeable than between 76F and 77F). Plus it’s fully compatible with Kelvin!

    1. Celsius is a supplementary unit, so its SI labeling isn’t so problematic IMHO as it is overworked to conform. It is worse when US “mt” is “metric ton” while MG is “milligram” instead of mg for milligram and Mg for megagram (10^6 g).

      But if we are going to be purists, we can note that K stands for kelvin. This is a feature in order to distinguish it from the person, as per the usual SI nomenclature.

      I note that outside of biology and weather doubling suffices. Else my trick, since I can never remember the correction factor, is to remember that Fahrenheit is a scale for outback horse owners. (Actually vets before thermometers.)

      So 100 degF ~ temp of large mammal ~ 40 degC. (2T + c) = 80 + c = 100 -> c ~ 20.

      Correct within a factor of 2.

  5. Made me laugh!

    Remember 61F is 16C & 28C is 82F.

    I always used to know if it was Farenheit for the weather apart from when it got to freezing, then somehow ‘centigrade’ as we used to call it took over. Now I prefer the Celsius scale.

    However, I would not say 0C is cold, but then I like the weather cold & damp because I am a bit strange!

    1. Or Estonian. Yeah, that’s crazy. I’ve been in a few of those saunas and when the women aren’t around, it usually turns into some kind of unstated competition to see how hot they can make it before everyone has to escape. 😛 It’s just crazy to be sitting in a room that’s frickin’ 210 degrees Fahrenheit! Breathe slooowly so you don’t burn your lungs… 😛

        1. No, I don’t think that is possible. Your epitheliums probably get a worse hit by a shot of whiskey. But you can start to get skin burns, I think, if you have trouble sweating (a few percent of the population).

          And you can loose control of your core temperature, same as in how weather, for a number of reasons involving medical conditions as well as unhealthy motivation. They stopped the sauna competitions in Finland after a guy died.

          1. Not definitive I know, but Wikipedia has this information about the one of the two finalists who survived the 2010 World Sauna Competition.

            “Kaukonen woke up from a coma two months after the event. His respiratory system was scorched, 70% of his skin was burnt and eventually his kidneys failed as well.”

            The other finalist died on the spot moments after the judges dragged him from the sauna. Though he cheated by using a strong pain drug and local anesthetic cream which contributed to his death.

            The rules specify a sauna temperature of 110 C and .5 liter of water every 30 seconds.

            After a little bit of reading I feel comfortable claiming that brief exposures to sauna’s in the 100 to 110 C range should not cause serious damage to a healthy person, but exposures of 5 minutes, especially several exposures within a day or two, can cause serious damage and even death.

            Not saying people who want to do that shouldn’t have at it, but damn. If I am risking serious damage or death I want some adrenaline and the satisfaction of executing some difficult skill well enough to have survived!

    2. Mostly swedish I think. The fins go in for comfort as far as I know. This is ~ 80 degC for shorter times, but somewhere between 60 and 80 degC if you are going to be social. I.e. hotter than circulated hot water should be to avoid scolding, hence you need a sauna aggregate of some form.

      Unfortunately Sweden never standardized over places and generations, so you have ~ 80 degC in most places – while some go nuts.

      100 degC isn’t deadly until you loose your core temp regulation. (Say, by drying out.) But it isn’t good either even if your skin temp is a lot less.

  6. We seem to have here a tradition in great British style … if its cold we use Celsius if warm Fahrenheit ….

    -5C sounds really cold … but 90F seems warm!

    (Don’t ask what we do in between …!)

    1. The newspapers are doing exactly that today – using Farenheit – as it will be up into the 80s this weekend in parts of the British Isles.

  7. Although I work with centigrade (Celsius) temperatures in science, I never have managed to absorb them directly because I was raised on Fahrenheit.

    All it takes to absorb them directly is living for a full year in a country that only uses Celsius (i.e., almost anywhere but the US). Then you know pretty thoroughly what each temperature feels like.

    Each increment of 5 degrees Celsius corresponds to an increment of 9 degrees Fahrenheit (exactly). I found it pretty easy using this to memorize a table of the Fahrenheit values corresponding to integer multiples of 5 degrees Celsius. To interpolate, add (or subtract) 2(4) degrees Fahrenheit for a shift of 1(2) degrees Celsius, and that will give the right answer rounded to the nearest whole number.

  8. I’m from the UK to and I’ll like to ask a few questions from the OP.

    1, What’s a heat wave.

    2, When did it ever stop raining.


    1. Are you forgetting? Up until late May we had 27 months with 20% less than average rainfall in the UK & no doubt other parts of northern Europe, & were entertaining the prospect of a serious drought.

  9. I dont get Farenheit or imperial at all. Grown up on celcius. at sea level, 0C= freezing point of water, 100C= boiling point of water. 37C= body temperature.

  10. As a herpetologist, I maintain that temperatures below 0 C don’t exist except inside tissue storage appliances.

  11. I can remember going ‘cold turkey’ in the early 70s in Australia when we went to metrication. Our currency went from Pounds, shillings and pence to Dollars and Cents in 1966. And the rest of the changeover unfolded out over a few years. As a teacher of wood and metal technology in high school in 1972 we were simply required to work everything in millimetres, vehicles went to kph, etc etc. It really didn’t take long to convert. And metrication is quite a deal easier than Imperial measurements, on a base 10 as it is.

      1. The size of the containers didn’t change much, but everything was/is labled in ml and l.

        AFAIK Europe did basically the same thing. Beer may still be served in the same glasses, but the line on the side says 0.5L instead of 1 pint.

      2. 1/3, 1/2, 1, 3/2, 2 L are popular liquid containers – 0.5 L for pubs if they are not cheap and give you a 0.4 L glass.

    1. California tried “metrification” in the 1970s on the road distance signs, giving KM as well as miles. They gave up pretty quickly, but they forgot a sign on Highway 88 near Kirkwood (ski) for many many years.

      Metrification was touted as inevitable in the 1960s and it received angry pushback. Politicians were as against it, as the Republicans are against evolution. It was a “third rail” (electrified) issue: do not touch, or, you die.

      1. I remember back in 2000 when George W. Bush was informed that Social Security was the “third rail” of American politics.

        He wanted to know what the other two rails were.

    1. Sorta. Converting C to F is only useful because you know what F means (e.g. 68° = a comfy room temperature). So skip the middleman and learn the “meaning” of C (e.g. 20° = a comfy room temperature). 😉

      1. I’m sorry, but 68° isn’t comfy, it’s freeze-your-balls-off cold!

        80°, now that’s comfy — especially when summer starts to hit its stride it’s warming up above 115° outside (and maybe dipping below 100° for the overnight low).

        I can tolerate 68° in the winter, and that’s where I keep the thermostat then…but that means that it’s probably only getting up to the lower 40s outside, and all the carbon dioxide has frozen out of the air at that point or something. I don’t know — all I know is that prolonged exposure to those temperatures can kill a human in a matter of minutes, so I won’t risk it.



        1. Agree with the RH=0 comment.
          Depends on whether you are moving or not. 68 is wonderuflly comfortable for walking and working.

          Depends on body size and metabolic rate as well.

          As Norwegians say: No such thing as bad weather, just bad clothing.

          1. As it happens, I’m deep in a biography of Roald Amundsen, and he and his comrades seem to have been the embodiment of that principle.

            By the way, if you want to have fun with sub-zero temperatures, get Roland Huntford’s “Race for the South Pole – The Expedition Diaries of Scott and Amundsen” and plot the temperatures and respective comments for identical dates. It appears Amundsen’s main problem, even at -40°C, was — sweating. The poor Brits were freezing their bollocks off. It seems your ideology will influence a lot more than your perception of temperature.

            1. IIRC, Amundsen studied the Inuit in Canada’s north for a considerable time, and adopted the parka and oversized pants, open at the bottom, to get rid of body moisture. The Brits did no such thing: standard uniforms and all that as your basic operating kit, and then add on top of that (ill-suited) clothing.

              1. And they were still trying to climb Everest in tweed sport coats in the 1920s! (You can take nothing away from their courage and persistence though!)

    2. LOLcats (with captions) are heavier than cats – who knew?

      Uncomfortable zone:
      15 deg C is jacket weather if you bike.
      10 deg C is jacket weather if you walk.
      5 deg C is jacket + cardigan weather.

      ~ 0 is no weather.

      – 5 deg C is when you start to see your breath at exhaling.
      – 10 deg C is when your nose starts to freeze at inhaling.
      – 15 deg C is no weather to be out breathing in.

  12. There was a great report on NPR’s Talk of the Nation program with Chicago’s “sustainability officer” describing what was being done in Chicago as things get hotter, wetter and colder.

    She talked about paving alleys (more in Chi Town than any other city) with a porous asphalt that lets the water seep back into the water table rather than running off into the sewer.

    Planting trees and different types of trees as it’s predicted that Chicago may be more like Atlanta in 30 years. Encouraging green rooftops. (City Hall has prairie grass growing on the roof which keeps the building cooler and cools the surrounding area)

    Chicago’s water department has been keeping up with the science and implementing changes for decades and is probably the most advanced water department in the world.

    Worth going over to NPR and listening to the report from Wednesday, July 18.

  13. Celsius and Kelvin make more sense than Fahrenheit (and I like that Kelvin has no negative numbers). Having grown up in the US as well I have to do the conversion, too.

    Just had a random thought: What if Fahrenheit 451 was instead named Celsius 233? It doesn’t have quite the same ring to it, though that’s probably just due to familiarity with the title.

  14. A Canadian friend of mine once told me that, over most of the range of temperatures experienced outside, “double it and add thirty” is a fair approximation of Celsius to Fahrenheit if you don’t want to multiply by 9/5 in your head. As you head to the extremes however, the approximation gets less and less accurate.

    1. I learned it as: double it, subtract 10%, add 32. Same number of steps as x9, /5, +32 but much faster to do in your head.

  15. Hm. I vaguely recall the Saturday morning cartoon PSA “Super Celsius”, which also gives the “37 is your normal body temperature” (98.6) reference conversion.

    Oddly, I can’t turn up either the video or the lyrics on-line. I guess the “Metric Marvels” never made it quite as big as “Schoolhouse Rock” did. I haz a sad.

    1. Of course, that conversion violates the significant figures rules. The idea that “normal” body temperature is precise to three significant digits is a myth that arose from people not understanding those rules.

      1. The conversion is exact; and correct, to the significant figures of the original Celsius. It’s the Fahrenheit value that has too many digits — but it’s well known to those too many digits, and thus the conversion rule remains useful.

  16. I thought of a simpler way to convert Celsius to Fahrenheit.

    Since 9/5 = 1.8,
    double C temperature
    move decimal one place to left (take 10%),
    subtract this from the doubled value,
    add 32.

    What I like about it is that it is exact (though I usually drop a place in the subtraction since it’s not significant anyway).

    Example: my processor is 87C right now:
    double 87 => 174
    10% => 17.4
    174 – 17.4 ~= 157
    +32 => 189F

    I tried to find a similarly easy and exact F->C conversion, but all I came up with involved an infinitely repeating 90% correction, which was deeply unsatisfying…

    Is it weird that I am so satisfied by the exactness even though I don’t use it?

    1. 5/9=.555…=1/2+1/20+1/200+…


      Is this what you came up with? It’s infinite, but it gets fairly accurate fairly quickly.

  17. I owe much to the 81 year old Anthropology professor who asked (among many facinating questions), of what temperature (F) will the human body begin to shiver, if laying on the floor naked.
    Hint: As a lap swimmer I knew the answer.
    It’s an interesting trivia question I’ve asked over the years which most people guess low.

    1. “Hint: As a lap swimmer I knew the answer.”
      You spent a lot of time naked on the floor getting laid?

      It’s going to depend on a lot of factors, such as what the floor is made of, the person’s unique physiology, and how vigorous the lay is. But it’s probably around 80 degrees F. Even higher if it’s a wet floor.

  18. I’m going to dispute the “dead…dead” labels on the Kelvin scale. It’s an axiom of emergency medicine (and cryonics) that you’re not dead until you’re warm and dead.

  19. º is the ordinal indicator. The degree symbol is °. I only say this because the ordinal indicator has a line under it in most fonts, including my RSS reader’s.

    In HTML, you can use ° to avoid confusion (or maybe °, I’m not sure if WordPress escapes ampersands in comments).

  20. I use benchmark temps (that are significant for personal comfort):

    -40°C: Same as Fahrenheit! Yay!
    -20°C: Still flipping cold (-4°F)
    0°C: Freezing point
    10°C: 50 — cool but not too bad
    20°C: 68 — my favorite!
    30°C: 86 — too hot
    40°C: 104 — waaaaaaay too hot
    50°C: 122 — forget it

    These temps are ALL significant for those of us crazy persons living the the US midwest. (No kidding. Well, OK, 50°C it taking it a bit over the top for the midwest; but all the rest!)

    1. Yes, C makes much more sense. I present it to Americans this way:

      0 – freezing
      10 – cold
      20 – nice
      30 – hot
      40 – effing hot
      50 – this is nonsense

      which is so much more logical than

      0 – really cold
      32 – freezing
      100 – hot


  21. Everyone here has missed out one very important measurement of heat – Scoville scale !

    Got some Insanity Sauce that is so bloody hot that the most minuscule drop is enough!

      1. Everytime I pose that question – and I’ve asked many – the responses are always much lower. But jump into a pool that’s 81 degrees F and it feels chilly until you start swimming.

    1. I recall reading that the native people of Tierra Del Fuego had no clothing to speak of, and maintained their body temperature, even in sleet and snow conditions, by internally burning massive amounts of calories compared to humans living in temperate climes.

      1. And freezing their miserable bollocks off!

        Just shows what humans can stand if needed. Reminds me of the Scndinavians moving to the Faroes, Shetlands, and Orkneys — tells you something (really bad) about the conditions back home!

  22. How can have a scale saying 0 C is fairly cold? 15 C is fairly cold. 0 C is freezing. Maybe you should move to a place with a more civilised temperature range.

    1. Aren’t we a versatile species?
      One man’s ‘below freezing’ is another man’s brisk constitutional out on the vidda.

      Friday, Dec. 8, 1911
      A: We had the best weather for a long time. Sunshine and almost calm. -18°. It was pure summer inside the tent. Everything of ours that is damp, dries in the course of a few hours.
      B: 88°25′ 17 -18.5. The greatest day we have had for a long time, calm and flat and fine, a little fog in the morning which lifted.

      Saturday, Dec. 9, 1911
      A: Th weather has been really good today. On several occasions the sun has been absolutely clear. -24° this evening. Light SE’ly breeze.
      B: 88°25′ -20.6 -24. Weather remained fine, afternoon overcast with cirrus clouds.

      Sunday, Dec. 10, 1911
      A: -28° Breeze from the south and crystal clear. It has been a little cool to go upwind, but nothing to make a fuss over.
      B: -28 -28 -29 Fine-fine weather but bloody stinging snow from the south.

      Monday, Dec. 11, 1911
      A: Fine weather again. Light SSE’ly breeze and -28°. Sometimes quite clear. Sometimes a ptach of mist. A lovely big ring around the sun.
      B: -28 -28 88°58′. Sunny weather SE wind.

      Tuesday, Dec. 12, 1911
      A: Lovely weather. Almost calm and partly clear. Ca. -25°.
      B: -24 -26 -26° 89°15 -15. The Pole is in sight. Fine weather, good observations.

      Wednesday, Dec. 13, 1911
      A: Our best day up here. It has been calm for most of the day — with burning sunshine.
      B: -23.5 -23.5. Sunny weather, fine-fine-day […]

      The next day, they reached the South Pole.

      A: Roald Amundsen diary.
      B: Olav Bjaaland diary (usually multiple temperature readings).
      Celsius temperatures bold, latitudes italicised.
      Original translation: Roland Huntford.

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