Celsiheit is back – but help is at hand

Just when we thought we had seen the last of Fahrenheit temperatures, a tabloid headline warns us against complacency and reminds us of those awkward conversions. Awkward no more, we are pleased to say, as Metric Views has learnt of a simple formula.

Headline from the Sunday Express on 5 April:

BRITAIN is about to get a long-awaited taste of summer with blue skies, sunshine and temperatures nudging 70F this week.

The Celsiheit thermometer immediately came to mind:

The Celsiheit thermometer
The Celsiheit thermometer

Interestingly, the internet version of the same paper had this headline:

Britain gets a blast of summer sun: Next week to bring blue skies and 21C.

Readers are invited to speculate on the reasons for the difference.

Of course, UKMA has always urged “Think metric. Don’t convert.” But there may be occasions when a conversion between C and F makes life easier, for example when the in-laws are over from the USA and can’t decide what to wear, when the kids can’t understand a tabloid headline, or when grandma insists on passing on a favourite cookery recipe.

For such circumstances, we can recommend this conversion formula, which was passed on to us by a contact in Canada, Alan J. Nanders. It is memorable, and the arithmetic is straightforward.

Alan writes:

For almost 50 years, I have been the lone voice in North America teaching the simple and easy-to-remember formula for accurately converting Fahrenheit temperatures to Celsius or Celsius to Fahrenheit. It is elegant in its simplicity, while totally avoiding the conundrum of when to add and when to subtract that confusing 32 degrees.

My “Nanders formula” is accurate for all values of conversion. Moreover, steps 1 and 3 are identical, regardless of which way you convert.


Step 1.   Add 40
Step 2.   Multiply by 5/9 (F to C) or 9/5 (C to F)
Step 3.   Subtract 40

So how long are we likely to be converting from C to F or vice versa?

The UK Met Office adopted metric measures for internal use early in the twentieth century, but the BBC did not include Celsius (then known as centigrade) in its public forecasts until 1962.  On the other hand, the USA shows no sign of nearing the end of its 150 year-long changeover to metric measures, and there are few Celsius temperatures in US forecasts. So the Nanders formula could be helpful for some time to come.

Alan has a fund of stories about metrication in Canada and some these will be the subject of a future article on Metric Views.

For the rational proof or explanation of the formula, contact secretary@metric.org.uk.

26 thoughts on “Celsiheit is back – but help is at hand”

  1. Face it, inconsistency has to be the UK MSM’s middle name. It’s quite common to see Imperial (USCS) and metric measurement terms mixed in the same sentence.


  2. That Nanders formula should never have been invented! One of the reasons why Canada uses Celsius virtually exclusively, in spite of the proximity of the USA and its constant bombardment of non-metric units, is that the old formula for converting was too difficult to use. Consequently, Canadians just said to themselves, easier to just get used to Celsius. Celsius is now so ubiquitous in Canada that, for example, the Toronto Star shows the daily temperature as simply degrees, without the C suffix.

    I just hope that not too many people, in the UK or Canada, get to see that Nanders formula – it could set us back 50 years. I’m sure that other old Commonwealth countries, even if they did see it, would not be so stupid as to start using it.


  3. Well, we thought this was a joke…..
    I have just been browsing gauges for car air conditioning. I notice that they do in fact have a dual scale. Positive pressures are in PSI, but when it goes to vacuum the same scale changes to inches Hg. Very interesting.


  4. To the original comment, it is true that US weather forecasts from the main stream media are almost always in Customary units. However, virtually all Internet services, from the National Weather Service, Weather Underground, etc, have a clickable link that converts the entire page to SI (sometimes quite well, sometimes with minor issues like decimal dust, no space between number and unit, etc.) I have no idea how many use it, but at least a few must or they wouldn’t bother. If you store the bookmark after changing the page, the choice is persistent.

    Actually, the Canadian weather service has metric primary but a link to convert the page to Imperial, although their media is metric only.


  5. It is interesting that Canada’s weather service includes a link to display Imperial measurements. Here in Australia the Bureau of Meteorology doesn’t include conversions to Imperial measures. (Check out http://www.bom.gov.au/)

    Maybe this is because we are farther away from the US.


  6. I don’t think the US is the direct cause but is very probably an indirect cause.

    The Canadian government either had more pushback from its citizens or was more willing to “wimp out.” Most Canadians live within a few (like 50?) kilometers of the border, visit the US, receive US radio and tv in addition to Canadian, etc. With that level of contact, and lack of a firm hand (look at UK), it is understandable that is been hard to completely phase out Imperial. Their roads are entirely metric. Their supermarkets have a lot of dual marked goods. They seem happy as long as the metric is there but the supplemental may be USC or Imperial.


  7. Question for Peter Goodyear@:

    Since I think Australia being far away from the USA has helped Australia convert to metric (as opposed to the partial metrication in Canada), has this gone all the way to Australians using metric for height and weight (both in the media and in personal conversations)? That seems to be the final area to convert for most people.


  8. Actually, there are some areas where the old units are used in Australia. The worst one in my opinion is the confusing mixture of acres and hectares in advertising rural lands. Some other goods are described using inches, like screen sizes http://www.binglee.com.au/tv-video/led-lcd-tvs or wheel diameters but mostly it’s metric all the way. In personal heights and weights, kilos have replaced stones and pounds, and centimetres are gaining ground on feet and inches for height. (Of course, everyone would know that a 6 foot man would be tall, but I think that most would be rather hazy about just how tall he was.) Another oddity is the continuing use of psi for tyre pressures (along with kpa).


  9. I understand John Frewen-Lord’s aversion to the much simpler “Nanders formula” for converting easily between Celsius and Fahrenheit temperatures in both directions. Being Canadian myself means that most of our Celsius temperatures have become experiential over the last 40 years of official Celsius, so that a reported 15 degree temperature means wearing a light jacket or windbreaker when going outside. And so it should be! – There are some exceptions though. Most Canadian homemakers will cook a dish in a 350 degree Fahrenheit oven and set their thermostats to heat their homes to say 70 degrees Fahrenheit. Much of this is connected to living so close to the “American elephant”, where they see little reason for giving up on Fahrenheit.

    My easy to use Nanders formula temperature conversion should also prove useful useful for at least North American students, who are still bedevilled in school and college exams trying to remember when to add and when to subtract that horrendous 32 in the confusing formulae used in most textbooks. – With the much greater advance of the metric system in Britain, there may therefore be understandably only of a more minor interest in temperature conversion here.

    Perhaps, the next time I should pick a better issue, such as the laughable and irrational paper sizes (such as 8.5 by 11 inches) that still seem to be used in so many countries for the simple reason that English is spoken there. Hopefully Britain, unlike the USA and Canada has discovered A4 (the old German Indusrtrial Norm DIN ?) and the beauty of the innate ratio of 1.41 to 1, being the square root of 2 to 1. – Perhaps a topic for another time!


  10. John Frewen-Lord states that the Nanders formula should never have been invented. Its chief flaw is that it is simple to remember and simple to use and will virtually allow anyone to to convert temperatures easily and accurately between Fahrenheit and Celsius scales. His assertion that Canada uses Celsius almost exclusively, despite the proximity to the USA, but because the old conversion formula was too hard to use, stretches one’s credulity. Most Canadians, myself included, have learned by experience over the last 40 years that when the weather report announces 15 degrees, then it is windbreaker weather, but at 30 degrees look for your swim trunks.

    At the same time, there will still be some continued need to do Fahrenheit and Celsius temperature conversions. Think of it the next time you plan a holiday to the USA, or you get an American recipe, or you work with Grandma’s cookbook, or you get visitors from overseas.

    Also, in America, many high school or college physics and general science text books still list the archaic and confusing conversion formula that leaves students sweating at closed book exams as to whether to add or subtract that confusing 32 degrees in the confusing and archaic conversion formula.

    By contrast, my Nanders formula of adding 40, multiplying by either 5/9 or by 9/5 and then subtracting 40 is elegant in its simplicity and lack of confusion. – So let us make life simpler and easier, while the need to convert temperatures will continue to decrease throughout the world.


  11. I had no idea your organisation existed.
    It’s great! The absurd inconsistency seen in the UK between different weights/measures/lengths etc etc is maddening! I can’t see why you are concerned about the so-called ‘Commonwealth’ countries though – that body is about as anachronistic in modern geo-politics as Fahrenheit and miles are to metric (ie normal) means of measurement. Let’s get the UK road signs in km first at least before worrying about them!


  12. Celsiheit has another meaning as well. Fahrenheit invented the mercury in glass thermometer, Celsius used this device for his scale. Those two pioneers of temperature measurement gave us the best of two worlds. So we have the paradox that millions of Fahrenheit thermometers (the device) carry the Celsius scale!


  13. Another OMG and LOL moment as the media try to do Fahrenheit / Celsius conversions either side of zero and struggle with temperature rise v actual temperatures!!!


    They just do not get that a 6 degree C RISE is not a 42.8 degree F RISE, it is about 10 degrees F rise. I do just wonder if they have any idea what they are talking about.

    I can’t really be bothered with sorting it out, maybe others can pick their favourite gripes.

    Here is one gem …. at least 3°C [37.4°F] above average.
    And another …. were 6°C to 7°C [42.8-44.7°F] above the long-term average,

    This is from the original and informative article that the Mail was trying to re-write so ‘we’ could understand it! “It’s about 20C [36 degrees Fahrenheit] warmer than normal over most of the Arctic Ocean, along with cold anomalies of about the same magnitude over north-central Asia, …”


  14. I agree with BrianAC’s lament that the press will confuse that, (quote): “a 6 degree C RISE is not a 42.8 degree F RISE.” (unquote).

    I think we all agree that the press is in error by confusing a movement of so many degrees on a temperature scale (i.e. a 6 degree change) with the value we give to a specific point of temperature found on a thermometer scale (here 42.8 degrees). This is an example of an untenable “apples and oranges” argument, that is confusing and wrong in logic. That error in thinking is quite unrelated to the fact that one numerical value refers to Celsius and the other to Fahrenheit. The basic thinking is wrong!

    Brian AC clearly understands that problem of logic here that the press incorrectly foists upon the reader. – Unfortunately, and with apologies to Brian, I do hold him at least partly responsible for perpetuating this muddled form of thinking in not properly separating and logically differentiating a movement of temperature by a number of degrees, with a point on the thermometer. – Brian’s contributing errors involve incorrect word order.

    In the above example Brian cited, he should have referred to a “6 Celsius degree RISE” to properly indicate it became so much warmer. In contrast, Brian’s wrong word order of “6 degree Celsius…” refers to a specific point on the Celsius thermometer, which is equal to a point of 42.8 degrees on the Fahrenheit thermometer. – Brian is partly forgiven for poor form, because he adds the word “RISE”, after “6 degree Celsius”, which would hopefully twig the scientifically attuned reader of his intent rather actual word order. (Before any other reader comes to the defence by pointing out the singular word “degree”, I will note that most often the “o” degree sign is used, which does not differentiate between singular and plural.

    I always warned my students that “10 degrees Celsius” is not the same as “10 Celsius degrees.”

    I agree with your lament Brian, but would encourage accuracy in style to help a common cause of better understanding and fewer errors of a dwindling press.


  15. @ Alan J Nanders says: 2016-11-24 at 03:00
    Thank you for that. I’m not sure what you mean, I am not a pedantic literary scholar. I will try to work it out sometime.
    I do expect media reporters to be a little more intelligent and educated than my over 70 year old brain has ever been, that is the main reason for my ire at this trashy reporting. I expect to be educated, not left wondering what they mean.
    If one were to refer to the original article, as I am sure the journalistic writer would have done, then there is indeed a scale there showing the relation ship between Celsius and Fahrenheit centred on zero, so no excuses whatsoever to get the figures wrong.


  16. To both Brian & Alan:

    In my opinion the only error the media made was making the decision to include Fahrenheit temperatures and not just leave degrees Celsius stand alone. Nobody actually does a manual conversion. Whatever software they are using to write the articles, has the ability to do unit conversions if it is activated.

    The conversion software does not know the difference between an actual temperature and a temperature difference. It is programed to recognise the string of a number and either the unit word or the symbol and do the conversion and insert it in the text.

    It is up to the reporter or editor to see the mistake and correct it. But, the moral of the story is to report it just in degrees Celsius and forget about Fahrenheit. Most readers however, never catch the error because they ignore the Fahrenheit anyway.


  17. @Alan J Nanders

    I also learned the convention that degrees Celsius was a temperature and Celsius degrees was an interval or difference of temperatures. Unfortunately, this was overturned in 1968 by Res. 3 of the 13th CGPM (see Appendix of SI Brochure). A temperature interval may be expressed in kelvins or degrees Celsius. Celsius degrees is an obsolete term. Nobody writes rules for Customary/Imperial, but US practice is to try to extrapolate. The fact that it is a difference must be conveyed in the body of the text, not the unit.

    I thought the older convention added clarity but the Lords of the SI thought otherwise.


  18. Apropos of mixing metric with Imperial (though not Fahrenheit and Celsius in this case) I was listening today to our NPR (National Public Radio) station, KUOW in Seattle, Washington. A reporter from the Seattle Times, Lynda Mapes, was talking about the struggle over the Trans Mountain pipeline from Alberta, Canada to Vancouver, British Columbia which is pitting a Native American tribe (Tsleil Waututh Nation) along part of the pipeline’s proposed route against the Federal government in Ottawa.

    I was surprised to hear Ms. Mapes talk about the distance between the proposed route of the pipeline and the location of the reservation of the tribe fighting against its construction as “less than one kilometer”. After all, she works for the Seattle Times and was speaking on the local Seattle public radio station, both totally in the USA. Why use “kilometer” instead of “mile”?

    I searched for her bio to find out if she was raised in Canada but could not find any info. I am guessing it was either that or she got information about the distance from a Canadian source. Either way it again demonstrates (amazingly, I still think) the power of metric road signs, which everyone sees every day. It is quite impressive that such a simple change can have such a profound effect in shifting people’s thinking towards metric as demonstrated but what has permanently happened in Canada (and also in Ireland).

    Too bad the Heath government dropped the ball and did not follow through with metricating road signs. If they had, it is likely the metric muddle in the UK would have been avoided altogether!


  19. I agree with Daniel that the only error was to use Fahrenheit at all. Only the US government can resolve that problem.
    The article has in fact since been corrected, so at least they are trying this year.


  20. Even at this late date a flagship news organization like the BBC is still doing everyone a disservice by giving temperatures in degrees Fahrenheit (lamely followed by degrees Celsius in parentheses) in their new reports. As an example, please see this article on canceled flights at Phoenix, Arizona due to a massive heat wave there:


    Most shameful of all, in one instance this news article even mentions degrees Fahrenheit with no mention of Celsius whatsoever!

    Temperature is one area (in addition to road signs, speed, and distance) where Canada (despite the huge drag on metrication imposed by the USA on that country) has been 100% metric since the late seventies. Fahrenheit disappeared completely and has been absent in Canada for almost 40 years now.

    To show how metric temperature is in Canada, I have stayed in hotels in Canada where the temperature controls were labeled only in Celsius. Since hotels cater to tourists and the majority of tourists come from the USA, it says a lot about the Canadian preference for metric (when not being shouted down by the “Imperial” influence of the USA) that locations catering to tourists nonetheless do not bother to provide indications in degrees Fahrenheit (even as supplementary units).

    Surely the UK, which does not have that same Imperial drag that Canada must face, could at least dump Fahrenheit once and for all!


  21. @Ezra:

    I have not in the last little while now come across anyone outside the media who uses F (one exception – an 86 year old friend suffering the early stages of dementia, and I think he can be forgiven for that).

    The most recent heatwave has seen everyone I have come into contact with talking in Celsius only. Only tabloid papers like the Daily Mail and the Daily Express insist on using F, sometimes on its own.


  22. Even the Guardian allows (at least on its Opinion pages) the monstrosity of Fahrenheit:


    When, oh, when will this madness end?

    To quote King Lear:

    No, I will weep no more. In such a night
    To shut me out? Pour on; I will endure.
    In such a night as this? O Regan, Goneril!
    Your old kind father, whose frank heart gave all—
    O, that way madness lies; let me shun that;
    No more of that.


  23. From the Link posted by Ezra:

    “For anyone interested in following and watching out for this, I have a suggestion: keep your eye on the fahrenheit as well as the celsius measurement it will mean more. I say this as a baby boomer who grew up with F rather than C; it was not until 1962 that the Met Office adopted celsius, and in my early childhood I acquired the instinctive feel that everybody then had (and people still have in the US), which told you that, in fahrenheit terms, 60 was pleasantly warm, and 70 was really lovely weather, and 80 was seriously hot, while 90 represented the sort of heatwave that was a major event. Anything approaching 90 would result in front-page headlines in the Daily Express proclaiming: “88 … 89 … 90! Phew! What a scorcher!”

    That was the point about the 100 figure. It was off the map.”

    I don’t know when this baby boomer was born, but even if he was educated in Fahrenheit, it would have been a breeze for him to learn degrees Celsius and after 1962, a difference of 56 years from 2018, there is no excuse for pretending not to be able to grasp degrees Celsius. It is much easier to learn degrees Celsius, than to memorise conversion factors so that each time one turns on the weather report, one has to back convert.

    The 60, 70, 80, 90 thing works just as well in degrees Celsius, actually much better. Below zero is freezing. 0 to 10 is cold to cool. 10 to 20 is cool to warm. 20 to 30 is warm to hot. 30 to 40 is hot to sweltering. 40 to 50 is sweltering to deadly. One can tweak this mnemonic to suit ones personal comfort levels.

    “Off of the map” could just as well be 35°C 0r 40°C or any temperature that one is uncomfortable with.

    The human body is a very accurate Celsius thermometer. It can discern a temperature difference of 1°C and everywhere in the world where the people use degrees Celsius normally don’t need thermometers to know the temperature. Fahrenheit users on the other hand can’t get an accurate assessment of the correct temperature using their body. They rely more on thermometers.


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