I am 1.79 m tall. But how should I say that?
Some years ago, I was being interviewed on a local radio phone-in programme, and I was asked my height. (Broadcasting presenters usually try to catch you out with such a question, hoping that you will inadvertently revert to imperial, and the presenter can then triumphantly claim that imperial is “natural”).
On this occasion I said “one metre, seventy-nine”, which seemed to satisfy the interviewer and we passed on to more interesting topics. However, later in the programme, after I was off air, a pedantic individual phoned in and said he had converted my figures into feet and inches and calculated that my true height was 3 feet 6½ inches. His reasoning was that in technical drawings “79” would represent 79 mm – hence, he registered “one metre, seventy-nine” as 1.079 m.
The presenter was bemused by this argument and gave it short shrift. It later transpired that the pedantic individual was a member of an organisation opposed to metrication, and he was obviously just trying to make trouble. Nevertheless the incident, contrived as it was, does raise a genuine difficulty: what is the best or most acceptable way of saying 1.79 m?
- “One metre, seventy nine” is by analogy with how we express prices – e.g. £1.79 would be pronounced as “one pound, seventy nine”. I would guess that, notwithstanding the pedantic trouble maker, most people would understand it in that way. It would be absurd to give your height precisely to the nearest millimetre.
- “One point seven nine metres” is obviously mathematically correct and is not capable of misunderstanding. However, with its use of the decimal point, it may sound somewhat scientific and user-unfriendly to persons unused to metric units.
- Another possibility would be “a hundred and seventy-nine centimetres”. This has the merit of avoiding decimal points and uses only one unit submultiple. This is by analogy with the practice of expressing fuel prices as e.g. “a hundred and thirty-nine pence” per litre.
- What should absolutely be avoided is the imperialist practice of giving both metres and centimetres as though they were different units – i.e. “one metre, seventy-nine centimetres”. This denies one of the key benefits of the metric system – namely, that it is based on a single unit for each physical quantity).
Acceptance of metric units in the UK is not helped by the existence of these alternatives (and there may be others) – people don’t know which to use. It would be better to standardise on one. But which?
On reflection, and despite my earlier response to the interviewer, my preference now is for Option 2. It is unambiguous and does not really place serious mathematical demands on the listener. I am not in favour of dumbing down the metric system to approximate it to archaic imperialist practices.
What do others think?
49 thoughts on “How should I say my height?”
I’m Australian. I would just say “one seventy nine”. It’s implied that I’m giving the height in cm and is consistent with the somewhat common convention of omitting “hundred” when stating numbers. For my own height, 201 cm, I generally just say “two oh one”, or else just round it to “two metres”.
Back in January 2009, I submitted an article to MV, and was published here: http://metricviews.org.uk/2009/01/metric-user-friendly/
In this article, I expressed the view that the metric system needs to be more ‘user-friendly’ if we want the general public to embrace it. I don’t consider this however as ‘dumbing down’.
I suggested that a person’s height could be expressed verbally as one-seventy-nine. Whether the listener thinks in terms of metres or centimetres, it amounts to the same thing. Implicit is the decimal point if thinking metres.
And it cannot be challenged by metric opponents, unless they challenge all such usage.
Of course it’s simply ‘one seventy-nine’. I always say ‘one eighty-four’ and not once has some nutcase mistaken that to mean one metre and 84 millimetres.
I don’t see what technical drawings have to do with it or why going from metres you’d skip centimetres and go straight to millimetres…
Two ways come to mind. “one point seven nine metres” is correct, as is “one hundred and seventy nine cm”. “1790 mm” would be excessively precise.
“one metre, seventy-nine”, I would say is totally meaningless. This is what the commentators use in athletics and as your article says, this would be 1.079 m, and introduces my pet hate, two different units of measurement, aka the Imperial system.
I work in architecture so I’m more familiar with using millimetres than centimetres but I usually give my spoken height as 175cm and sometimes just give it as 175. If I have to write it down, on a form for instance, I write 1.75m. Similarly, if someone asked me the time in the evening I’ll say it’s seven or eight o’clock. If I needed to make it clearer I would say seven or eight o’clock in the evening but I would write it down as 19.00 or 20.00.
Option 2 is the clearest and therefore not unfriendly. This is how I would say it to myself while comparing containers when shopping in a grocers. Option 3 is the one used by health professionals.
I’m American, so minor cultural differences. I certainly would have correctly understood “One metre, seventy nine” as 1.79 m, but I probably would have said “one point seventy nine meters.” For me, the other alternative would be “one hundred seventy nine centimeters.” (I would omit the “and”). Like most British/American differences, I think we would understand each other correctly.
The use of the unit as an implied decimal marker seems pretty reasonable in casual (English) speech, with anything following as the most significant digits of the decimal fraction. I have to disagree with your pedant. The zero in 1.079 m would have to be CLEARLY stated in word form, and only “one point ZERO seven nine meters” would do. The other problem with his absurd assumption is that millimeter precision in human height makes little sense.
Had you been on an engineering drawing (1790 mm), the unit is not required, and I suppose one might say seventeen hundred ninety, or one thousand seven hundred ninety, or simply one seven nine zero.
Another point, in track & field, performance in the field events is stated in meters, to two decimal digits. I would assume there is a “standard form” in announcing the result to the audience, and this might be a guide.
One of the advantages of the metric measures, is that they can be adapted and expressed in different terms. For example; 1.79 m can be 179 cm, or 1790 mm. However this can also be a disadvantage, because a single measure has a number of terms, and confusion can occur, not so much from the written term, but from the spoken one.
Another advantage of metric measures, is to be able to convert a term, or number, that has a decimal fraction, to a whole number. Converting to whole numbers, reduces errors, and costs, not only in the written form, but also in the spoken one as well.
Therefore I think a body height of 1.79 m should be 179 cm, but only in the context of body dimensions. In other contexts I would mainly use millimetres.
I would say 179 cm, as “one seventy nine centimetres”, or “one seven nine centimetres”. That is the more modern (short cut) wording of the number. Older folk are more likely to say “one hundred and seventy nine centimetres”. I think the word “point” should be avoided, when measures are spoken, and only whole numbers used, to remove any confusion.
I reckon either “one point seven nine metres” or “one hundred and seventy nine centimetres” are the best options.
In UK society where people are still learning metric it is better to emphasize the single unit form of expression. In countries where metric is well established the more relaxed form, such as “one metre seventy-nine” is OK because metric is second nature and the meaning is perfectly obvious.
But in the UK I think it is important to encourage people to move away from the traditional dual unit concept like feet and inches or stones and pounds. To do this it is better to avoid phrases like “one metre seventy nine centimetres”. Metres and centimetres are not mere substitues for feet and inches. The philosophy behind metric is fundamentally different to imperial and the advantages need to be demonstrated. Otherwise people will not understand the need for change.
Having lived in fully metric European countries for most of my life, I would say ‘one seventy nine’. That can be understood as meaning either ‘one metre seventy nine’ or ‘one hundred and seventy-nine centimetres’, which are the same thing of course.
Even in the UK I see no problem with making the transition to a more colloquial way of expressing the figure rather than dwelling on the decimal ‘point’, so I disagree very slightly with the previous poster on that point (no pun intended). I would say the onus is one the person listening (and presumably asking what your height is) to understand what you mean. By the same token, if someone in imperial or American customary mode tells me their height is ‘five ten’ I am expected to understand they are talking ‘feet and inches’.
Since ‘one seventy nine’ cannot mean anything other than ‘one point seven nine metres’ I see no need to say it any other way.
Born and raised in Europe I’d say “one metre seventy nine” and would write it 1.79m not 179cm
Why are whole number measurements inportant?
I am 1.79 m tall. But how should I say that?
Many people, when seeing 1.79 m would say it as they see it.
“One point seven nine metres” or “one metre seventy nine” or maybe incorrectly “one metre seventy nine centimetres”
Those that get it wrong and say “one metre seventy nine centimetres” or “one metre and seventy nine centimetres” are stepping back to the Imperial multi unit measurements, because they are confused, between the decimal fraction, and the measurement. Most know that the one in 1.79 m is a metre, but how do they explain the fraction. What is the 0.79 m ? The 0.79 m is a decimal fraction, of a metre, but we dont measure with fractions of a metre, at least not in the metric system. Most people familiar with metric units, would think that the 0.79 m is 79 centimetres. Therefore when 1.79 m is seen, they think in two units, metres and centimetres, and this can cause them to speak in two units. “one metre and seventy nine centimetres”. Multi unit measurements should be avoided, when thinking, when writing, and when speaking, metric measurements.
I am 179 cm tall. But how should I say that?
Most people, when seeing 179 cm would say it as they see it.
“One seventy nine” or “one seventy nine centimetres” or “one hundred and seventy nine centimetres”. 179 cm is a whole number, with one measurement unit. By removing the decimal fraction, there is no confusion caused by the decimal fraction, and what it represents. Also, most people when seeing the whole units, would think in, write in, and speak in, whole units.
If you choose centimetres, for body height, you have immediate advantages.
1) All measurements are whole numbers, so there are no fractions.
2) All measurements can be entered into a calculator without any conversion.
3) There are no occasions when you have to slide decimal points backwards or forwards.
Using whole numbers with one measurement unit reduces errors, which in turn reduces costs.
The main reason I’m asked my height has been during visits to the GP or hospital. I’ve always said ‘one eighty-three’ (in my case) and have had a reaction of pleasant surprise from NHS staff, presumably because they don’t then have to look up a conversion table before recording it.
I’ve always wondered what the police reaction would be if, as a witness to a crime, I estimated a person’s height in metric. Would they think I was joking, or are they expected to record it in metric units anyway? Just glad to say that I’ve never been in that situation! Obviously (and sadly), newspaper reports always use imperial units for an individual’s height. I personally would struggle to narrow a stranger’s height to below average, average or above average anyway.
I was in the position you described. I witnessed an assault, and called the police. I gave my statement, and then some weeks later was subpoenaed to appear in Crown court. The counsel for the defendant asked me how far away I was from the assault when it happened. I replied, “About four metres.”
The judge said that, while he acknowledged that I, as a surveyor, I was used to working in metres, the jury was likely not that familiar with metric measurements, as he himself wasn’t, and would I convert my metres into feet and inches. I actually wondered whether to challenge the judge on this, but thought better of it. I still qualified my conversion by saying that this was an approximate conversion only, and that my assessment of four metres was, as far as the court record was concerned, the only figure I would stand by.
The judge gave me a long look, and instructed the jury to use the feet and inches figure when coming to their verdict.
I had a similar incident happen to me when I went bowling in Japan, I was asked my shoe size, I answered 10, however they used cm luckily I had a label indicating 28.5 cm. I now use this measurement when possible and say 28 and a half cm or 28 point 5 cm with height i say one hundred seventy six cm as 5 ft 9 and a quarter inches doesnt sound as nice!
I always say one metre sevently, which is normally results in a puzzled look.
For my own height I’d say “one metre eighty-four”, as for me 1.084 m would be “one metre zero eight four”
Goodness me, it never occurred to me giving one’s height could be a matter for great discussion. Like others here who are entirely comfortable using metric, when a nurse asked me my height recently I just said “one seventy”. It flows naturally and I feel confident the nurse didn’t interpret it as “one foot seventy inches”, “one hundred and seventy millimetres”, or anything equally daft. As for “one point seven metres”, surely no-one looks at a price in a supermarket and reads it as “one point seven pounds/euros/dollars/whatever”, so why do the same with height?
The answer to that is in the lead article.
It is because the ‘other lot’, those that oppose metrication, take delight in nit-picking the way metric is used. This pedantic approach is therefore required.
This further exacerbates the problem of the metric / imperial divide. It also prevents a set of colloquial sayings from coming into public usage in the UK in general. This then hampers its public appeal.
They well know this, which is why they do it. Should we respond or just ignore it?
I say just ignore them. If you pander to their erroneous arguments you are just prolonging those arguments. Sure, if someone challenges you directly then point out that they are simply mistaken. In the example given in the article, giving your height to another person has nothing to do with defining a length on a technical drawing; it’s a matter of context. Technical drawings are typically presented in millimetres. Traditionally (at least in my own field of engineering) that would have been thousandths of an inch (“thou” in the UK, “mils” in the US), but I doubt anyone has ever given their height to someone in thou, so why would they give their height in millimetres? Moreover, I’ve never seen a technical drawing that defines lengths in yards and thou, or one that uses a mix of metres and millimetres. The so-called pedant’s argument is utter nonsense.
Some progress at my local doctors surgery this Autumn. I had complained about them automatically converting metric height and weight into ‘English’ units so I could understand them. This year at the annual jab and weigh in I was asked for help to measure some ones height. It was of course “1.7” or whatever. The obvious question came “what’s that in feet and inches”? “I have no idea” I lied convincingly. He then asked the same question of the nurse at the computer “I have no idea” she replied. “Oh, OK 1.7 metres it is then”, he mumbled. At least he got the message that some of us do use metric, maybe the surgery has also.
In undergoing a health check recently at my surgery, the nurse measured my height and weight in metric units. Before she had a chance to ‘convert’ them to non-metric units, I entered them into my phone’s calculator to check my BMI. I then said to her that my BMI works out to 22.3, which she said was very good.
In all of this procedure and subsequent conversation, there was no mention of imperial units. Whether she recognised that I knew my statistics in metric, or she just couldn’t be bothered to convert them, I am not sure.
Beyond the question of how do you state the height in metres or centimetres, I am moved to ask how is height (or distance in John Frewen-Lord’s case) usually referred to in colloqiual English in Britain. This is obviously a linguistic question but I discovered this discussion as I am trying to write a science-fiction story where the standard of measurement is metric. I am American and don’t have this issue but now I see that even in a country where the standard is metric, it would seem that the imperial measurements, for height at least, are still predominant. Is that thecase?
I think you need to qualify that. In SOME English-speaking countries, imperial may linger for height: UK and Canada, yes, Australia, New Zealand, etc., not so much. Most Germans (except maybe the elderly) speak excellent English as a second language but are unlikely to be familiar with Imperial measurements.
How far in the future is the story set? What are your assumptions on how the world got from now to the time of your story. You need to establish your assumptions and write canon for your universe to lay a foundation for the story. Even the US might be metric by then. I’m American and I’m 194 cm, which I would say as one-ninety-four if I thought centimeters would be understood, one hundred ninety four centimeters otherwise. Of course, the DMV makes me say 6’4″ every four years.
Metric is a one-way street and it is simply a matter of how far have we gotten, protest groups like BWMA and ARM notwithstanding. I would look to Australia and New Zealand as the English-speaking countries that have most successfully metricated, and NOT the UK (or US).
Colloquial English in Britain:-
For an adult, you could try “one eight” meaning 1.8 m (180 cm); avoid ‘six foot’!
In a doctor’s surgery, or in a police description, “one eighty” provides more precision/accuracy.
As long as the context is clear it will not be mixed up with, for example, ‘five eight’ which means five feet eight inches.
I’m American, and found this post when trying to figure out how to state a character’s height in metric in the book I’m writing. I think just “one metre seventy-nine” is perfectly acceptable, and I tested it by asking Google to convert “one metre seventy-nine” to inches, and it understood me perfectly, so I think it’s safe to say that your method is fine.
In China, these decimal values are usually announced with the unit name replacing “point”. We have been using a mostly decimal system for length in thousands of years.
For Example, ¥1.20 is “YI KUAI ER” (one yuan two), 1.70 m is “YI MI QI” (one meter seven) or “YI MI QI LING” (one meter seven zero), while 1.07 m is “YI MI LING QI” (one meter zero seven).
As I am not a native speaker of English, I guess I will just say it in the way expressing dollar-cent or pound-pence, like “One, Eighty-six” for my height.
I’m Canadian and live in Japan. I’ve never given my height in metres. In Canada, most people use feet and inches, but in situations that call for metric, I’ve always encountered only cm, so that I’m 176cm. Same in Japan: only cm.
I always thought one of the advantages of using metric was that we didn’t have to give measures in two kinds of units (feet & inches, pounds & ounces). I guess this mentality is so strong with those not used to metric that they think they must use “metres and centimetres”, when they could just use centimetres. It’s simpler, and absolutely unambiguous.
No one actually gives their height in metres and centimetres at the same time. It is one or the other. The beauty is that if you stated your height as 1.76 m, the persons hearing it can take it as it is or mentally convert to 176 cm. There is no confusion, both are mutually understandable.
Feet and inches presents a problem. some one giving a height in feet only or inches only would cause confusion as there is no way to easily convert those values to feet and inches. Also when calculating BMI feet and inches are useless. BMI works best when kilograms and metres are used directly.
My stepdaughter recently asked a similar question on Facebook… the range of responses and the number of people in their late teens and 20’s who could not get their heads around only needing to use a single unit was truly depressing.
I Say feet and inches, always will.
“I Say feet and inches, always will.”
And what does that prove? I would say mine in metres if I’m asked, but haven’t been in years, if not decades. How often have you been asked to state your height or do you volunteer it just so you can get the warm and fuzzies saying it?
I would say it in metres as a means to constantly improve my understanding of metres as well as being able to communicate with the majority population of the world. The more you use something the more proficient you are at it. It is the metric understanding economies of the world that are growing and those that know and can use the metric system as employable in the better paying jobs. The rest struggle just to keep a roof over their heads, healthy food in their belly and nice looking clothes on their back. It is your choice if you want a life of prosperity or poverty.
No Brit – of any age – would EVER give their height in metric measurements.
And I write as a teacher of 39 years experience: EVERY British pupil ALWAYS gives their height and weight in Imperial: feet, inches, stones, pounds.
Those from overseas uses Metric (but soon learn to drop that)
I find it amazing that Bryan Corbett has such advanced knowledge to know what units every Brit uses. Those people who involve themselves in health management and make use of a physical fitness club will use metric units for body measurements. An increasing amount of exposure to metric units in the outside world is reversing the 39 years experience Bryan claims to have.
Kilograms in the headlines (no conversions to pounds):
‘I was 39 kilograms’: Fitness model, 25, reveals
‘I wasn’t a happy person before’: MAFS’ Alycia shows off her incredible 42 KILOGRAM weight loss in jaw-dropping throwback snap… after cutting all ‘toxic’ people out of her life
Students today can’t relate to fractions and when encountered and convert to decimals.
“Today’s secondary school pupils were much more familiar with decimals than they were 30 years ago. On the other hand, fractions appeared to be much harder for today’s pupils, the study suggested. ”
“Thirty years ago, pupils would sometimes convert decimals into fractions to solve a problem, but those taking the tests now did the reverse, researchers found. ”
If people use feet and inches for height, it values given must be guesswork as those that can’t do fractions nor understand them are obviously less likely to be able to measure using them or have garner any useful meaning from them. They may repeat a value they have guessed or have been told, but could never measure for themselves.
The kilogram is gaining in popularity among the public. Clothing shops advertising “by the kilo” are popping up everywhere.
People are using kilograms openly in speech.
“‘They weigh a kilogram EACH!”
So Bryan, the switch to the metric system among the young and the public in general is happening. It might take a generation to completely wipe out pound/feet usage, but the trend is in the direction of the kilogram and metre, not the other way around.
You speak for yourself Mr Corbett, you don’t speak for Every pupil only those who have contact with you. As far as overseas? Every overseas person I have contact with still uses metric for weight and height (as do I), the ones you are in contact with probably just use it in your presence just to stop you moaning and getting on your soap box.
@ Bryan Corbett says: 2018-03-31 at 16:12.
Moderators would prevent me from posting what I really think of this. That is indeed a pathetic indictment of your teaching skills then.
Why have you not been correcting that situation rather than seemingly extolling it as a virtue? Why do you not follow the spirit of the curriculum and teach the measuring system that has been the law of this land for over 50 years?
Even to the point of apparently enthusing over reverse educating overseas students. I am sure more of this will follow from others, a disgusting betrayal of your students and a scandalous misuse my taxes.
@ Matt Smitt says: 2018-04-01 at 13:10
Matt, I think you pretty much nailed it there.
If that post is indeed real and not just a wind up, they just use Imperial ‘to keep teacher happy’ and for no other reason. On the credit side it could be counter-productive as it would make them think how they use (or misuse) measure and revert more readily to metric, which is today in UK, very much on the increase in everyday life.
It’s a curious thing that height and weight are quite different. In Australia just about everyone dropped the stone decades ago while a lot of people still think of their height in feet and inches. However, official usage has switched to centimetres:
Missing persons: https://missingpersons.gov.au/view-all-profiles See the individual profiles.
Rugby League: https://www.nswrl.com.au/players/ See the individual profiles
There are, of course, other areas in Australia where the old measures are still used, like television and phone screen sizes.
“No Brit – of any age – would EVER give their height in metric measurements.
Unsupportable garbage, the usual hyperbole I associate with the Far Left and other assorted ne’er do wells.
“And I write as a teacher of 39 years experience: EVERY British pupil ALWAYS gives their height and weight in Imperial: feet, inches, stones, pounds.”
Everyone? Are you really sure you wish to make such a outlandish claim? If so, you are going to have to present evidence to back up your claim, otherwise you are just emoting on the subject.
“Those from overseas uses Metric (but soon learn to drop that)”
All in all, at best you are extrapolating from anecdotal evidence, always a risky move, or you are just blathering in the vain hope of trolling.
Saying “one metre seventy-nine” always implies 1 m 79 cm just by way of saying “seventy”.
Similar thing with saying “one (hundred) seventy-nine” which always implies 179 cm.
The only way you can imply your height in metres is by saying “one point seven nine”, “one metre seven nine”, or “one seven nine” for short. Since you’re reading the fractional part as a decimal set of numbers rather than whole numbers, it will always imply 1.79 m. The latter is the one I use when giving someone my height in metric units, since I always use metres in that context. It’s easier for BMI calculations, and it also avoids the whole non-power-of-3 set of issues.
As an aside, I don’t understand what the problem is with using millimetres. If it’s good for large numbers in engineering drawings, then it’s good for everyday use as well. It’s easy enough to round to the nearest 5 or 10 if “excessive precision” is the problem, the same way Mondopoint handles this issue. Saying “seventeen ninety” is just as easy as saying “one hundred (and) seventy-nine”, if not easier. It’s true that the full form of it would be “one thousand seven hundred and ninety”, but in the same way that people don’t refer to years by their full form, they wouldn’t for heights quoted in millimetres either (e.g., “twenty nineteen” instead of “two thousand and nineteen” for 2019).
‘Comparing the ease of using millimetres (with the engineering example), and the use of centimetres’.
I suppose if rulers and tape measures [in everyday use] were ONLY marked in millimetres then perhaps the general public might eventually get more used to using millimetres. However, I’m sure the use of centimetres is much easier for members of the general public.
Centimetres should only be used if the number is kept to a whole value. If there is going to be tenths of a centimetre, then the correct usage would require millimetres. A lot of products sold in the US have inches first and centimetres in brackets, but always to the tenth of a centimetre which looks ridiculous, especially when you encounter numbers like 88.9 cm instead of 89 or 889 or 890 mm.
I almost feel the centimetre with tenth parts is done to make metric units look horrible to American eyes.
@Mary: This is actually the case in many countries such as Australia, New Zealand, and Japan. Since the building industries there exclusively use millimetres, they can avoid dealing with mixed units or unit confusion, so they use millimetre-only rulers and tape measures. This principle has been extended to many others parts of life in Australia and New Zealand as well, which is why centimetres are basically only reserved for height, and millimetres are used in most every other part of everyday life, as they have the added benefit of whole numbers as well.
That said, “the use of centimetres is much easier for members of the general public” is not really true, considering the point about decimals points and such. There is a myth about using centimetres being better because it produces “nicer numbers” or “values that the public can mentally grasp”, but this is unfounded when you consider things like 4-digit years and prices for electronics and other merchandise and 5- to 6-digit prices for homes all of which are common encounters for the general public.
@Daniel Jackson: Yes, that practice is ridiculous, but it’s also obvious that the companies/people who do it are merely converting from US customary units and are not familiar with the metric system. Centimetres shouldn’t be used at all; there’s no use for them. In fact, there’s no reason to be using any centi-, deci-, deca-, and hecto- prefixes for anything (except maybe hectares for the last one, but that’s debatable as well). It greatly simplifies the metric system, makes it easier to teach, and makes it conform to the 3-digit groupings people use as thousands separators as well as the word-equivalents such as “thousand”, “million”, “billion”, etc.
I’m not quite sure what you mean by millimetre and centimetre only rulers and tape measures. Every tape measure and ruler I have is both millimetre and centimetre marked. Some rulers mark every 10 millimetres in increments of 10 and others mark them in increments of 1. Are you referring to those that use increments of 1 as centimetre rulers? If so, I don’t see this as a major issue. In either case, the other can be mentally referenced without an issue.
One can easily in one’s mind drop the zero on those that are in increments of 10 and can easily add the 0 to those in increments of 1. This is totally different than say mentally convert a reading in inches to feet and inches and vice versa.
As I mentioned centimetres can be used but, should only be used if the numbers are restricted to whole values.
My feeling on the use of large numbers is to restrict them to a range of 1 to 1000 and choose the appropriate prefix to match. I loathe describing the distance to the moon as 384 000 km, when 384 Mm would be better and the distance from the sun to the earth as 150 Gm instead of 150 000 km. There is no sense in using a plethora of counting words and/or zeros. Using the other prefixes gets one use to hearing them and comfortable knowing them. We talk of megabytes and megahertz, we can talk of megagrams and megametres as well. We talk of gigabytes and terabytes, we can also be familiar with gigametres, terametres, gigagrams, teragrams, etc.
The four prefixes around unity do have a limited use and should not be discarded but used in those select circumstances where they are the most logical. The litre is defined as a square decimetre, thus the prefix deci has a use in this application. Even though I prefer the prefix kilo for use with the pascal for standard pressure communication, for now we still have the hectopascal which is exactly the same thing as the millibar, so hecto has a use. Also, you mention the hectare, which just happens to be exactly the same as the square hectometre. I have no problem describing areas in square dekametres, hectometres, kilometres, etc. Whatever it takes to keep the numbers in a format that eliminates counting words and zeros.
The problem with counting words, especially those beyond a million is that in many languages they don’t mean the same thing. Between a million and billion the milliard is missing and when used, the billion, meaning bi-million or 10^12 (10^6 twice, thus bi-). The -iard suffix adds an extra three zeros thus billiard means 10^15, filling in the gap. An octillion can be figured out from the prefix oct mean eight and multiplying it by 6, the number of zeros in a million to get an octillion of 10^48.
I won’t even get into the Indians using laks and crores.
The problem basically is that even in long-standing metric countries the kilometer is treated essentially as a base unit of long length. That’s why in French or German documentaries (for example) the distance from the Earth to the moon is given in kilometers rather than gigameters.
It will take a lot of new education on the part of children to get them to use prefixes properly and in all contexts. Meantime, I keep hoping the UK will finally ditch Imperial altogether and use metric in some fashion or other 100% of the time.
I’ve been saying for sometime that metric units are improperly taught. There is only one base unit for length and the prefixes are applied to keep the values in the range of 1 to 1000. In SI, there is no short length, no long length, just length.
Yes, I do mean only marked with millimetres (as in every mark indicates a millimetre progression), so a “major” mark would indicate “10 mm” instead of “1 cm”. And this actually is not a trivial issue; if one sees minor markings that all lead up to a “1”, one can only conclude that the markings up until then were submultiple (decimal) ones, which would mean the units are in centimetres and gets at the exact problem you’re describing. And it sounds incredible, but not everyone’s numeracy is up to the par where they can shift decimal places or drop zeroes, etc. Not having to do that at all is a great way to circumvent that problem. This is exactly why avoiding centimetres altogether is important.
I wholeheartedly agree with your points about using the full range of prefixes to avoid ridiculous phrases like “500 million kg”, “2 gigatonnes”, etc. When I meant discard, that’s essentially what I meant: they should be relegated to the scientists who are bothered with defining units rather than be present in the public arena (in the same way the general population seldom knows what a katal, henry, or candela is), and only be used if absolutely necessary or if they provide great benefit (e.g., square centimetres are much more useful and convenient than square millimetres or square metres). The hectopascal case is actually one of a failure: people at the World Meterological Organization (WMO) caved into the pressure of others who didn’t want to change from millibar-calibrated instruments, and so now we have an industry that’s standardized on “hectopascals” only in name. Basically everything is still measured and communicated in millibar, and this is still visible if you look at the atmospheric pressures reported by many weather outlets.
I would actually go further to say that everyone should avoid ridiculous compound units and unnecessarily “invented” units, such as “tonne” (the SI term is megagram), “kilowatt-hour” (the unit should simply be megajoules), “milliampere-hour” (the unit should be coulombs), “metric horsepower / cheval-vapeur / Pferdestärke” (the unit should be kilowatts), etc. Inventing new words not only confuses the general population, but also has no benefit, so it’s doubly bad.
The prefixes mega and micro were only introduced in 1873 and giga and nano in 1960. By this time the kilometre was so firmly established that there was no pressure for people to change to megametres or gigametres which is why kilometres stayed.