UKMA launches Measurement Units Style Guide

In an attempt to bring about some improvement in the sloppy and inconsistent way in which metric units are often written, the UK Metric Association has today (5 July 2012) published a “Measurement Units Style Guide”.  Aimed at anybody who uses metric units in their writing, the Guide is available in both hard copy and as a free download from the UKMA website.

UKMA is concerned that, although there is now widespread use of metric units in the UK – in the media, in official documents and in education (not to mention shopkeepers’ signs), they are often written in an amateurish and inconsistent fashion, importing some of the bad habits from obsolete measurement units.  Many organisations, although they strive to avoid spelling or grammatical mistakes, appear to tolerate or condone bad practice in the writing of measurement units.  Unfortunately, mistakes that appear in print tend to be copied by readers, and bad practice is thereby disseminated.  This lack of consistency does not help understanding or clear communication.  It also conveys the impression that metric units are unfamiliar and difficult rather than being instantly recognisable symbols that we all relate to.

It is believed that this inconsistency stems in part from the lack of easily accessible guidance or advice.  This Style Guide is intended to fill this gap.

In drafting the Guide, its authors were faced with a number of problems:

  • Many writers, especially professional writers, think they know how to write, and may resent being told by outsiders how to do their job
  • Others need to be convinced that there is a right and wrong way of writing measurement units – or that it matters
  • The media are in the business of communication and they therefore need to take account of their readers’ level of familiarity and understanding
  • Some areas of UK life such as road signs are still officially imperial, and it is difficult for the general media to discuss motoring issues without any  reference to imperial units
  • The failure hitherto of the education system over nearly 40 years to establish good practice in writing measurement units
  • Technical difficulties such as the absence of certain symbols from computer keyboards

The Guide has therefore had to try to strike a balance between – on the one hand – advocating adherence to the formal rules (as laid down by the International Bureau of Weights and Measures (BIPM) and endorsed by the British Standards Institution) and – on the other hand – being sensitive to the understandable concerns of professional writers and the constraints of the “two systems” muddle in the UK.

Whether the Guide has struck the right balance remains to be seen.  Purists may be disappointed that it accepts the necessity for allowing some use of “miles per hour” (mph) in motoring reports, or of “calories” in nutrition stories.  Others may worry that its dismissal of the Fahrenheit temperature scale may alienate some writers.

UKMA is at pains to emphasise that it is not the primary purpose of the Guide to persuade writers to change from using imperial units to using metric units.  As their press release commented, ‘That is a matter for the policy of the organisation they are writing for.  Rather its purpose is to help writers who want to write metric units correctly.  “After all,” added UKMA’s Chairman, “most people strive to avoid spelling or grammatical mistakes.  I hope our Guide will help them to avoid mistakes in writing measurement units”.’

Issues that the Guide deals with include:

  • When to use capitals and when to use lower case
  • Which metric units to use
  • How the metric system works
  • The difference between symbols and abbreviations
  • What to do about conversions
  • Avoiding mixing metric and imperial
  • Advice on punctuation
  • Common mistakes to avoid

Electronic copies of the Guide can be downloaded from the UKMA website at

The hard copy of the Guide is attractively printed in colour on A3 card folded to four sides of A4 and is intended as a durable reference card that writers can keep on or next to their desk.  UKMA can supply small quantities (up to 10) free of charge, but for larger quantities, it will be necessary to cover the costs, which are 30p per copy, plus postage.  (Please e-mail ).

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24 Responses to UKMA launches Measurement Units Style Guide

  1. Martin Vlietstra says:

    Good work Robin et al!

    One example that I like to use to emphasise the need to get the case correct is that a 1 mW power supply is sufficient for a hearing aid and a 1 MW supply is sufficient for certain classes of suburban train.

  2. John Steele says:

    This is an excellent guide. I like it better than NIST's LC 1137 which is also a guide for the media. I do have a few comments. Please remember I am commenting as an American, and while intended to be constructive, there may not be 100% agreement.

    Page 1
    1) In the chart, I would suggest "L" be offered as the only symbol for litre, and the "l" explained somewhere in text.
    2) The bar is less accepted with the SI than the litre, hectare, and tonne (table 8 vs table 6). I suggest it be omitted entirely. Is the bar much used in the UK?
    3) On spacing, I would strike "Where there is room." This is a particularly British error, the space is always required between number and symbol, you wouldn't write twentyfivekilograms. If this is a likely error in spite of your recommendation, it is particularly important to recommend L over l as the litre symbol. If you agree, there are some similar phrases on other pages.

    Page 2
    4) On symbols, I think something stronger than "used in preference" should be said. In the SI, invented abbreviations are unacceptable. That is why they went to the trouble of defining symbols. You should probably make two further points:
    a) Symbols are never used stand-alone (without a numeric value)
    b) With a numeric value, symbols are preferred to words for the unit because they are uniform across all languages, words are not.

    Page 3
    5) On temperature, I was going to say that Americans don't necessarily need conversions, but if you omit the Celsius, we would likely misinterpret. Assuming a numeric value is being given, °C takes less room than degrees, and makes it clear to everyone.
    6) On mixing units, I am not troubled by the 40 MPH or recommendation for kilometres per hour in parentheses. I would certainly omit the reference to metres per second. No nation uses this for vehicle speeds; it serves only to confuse the issue.

    7) I would add the code for the non-breaking space (ALT-0160) to the table

  3. David Brown says:

    A couple of other “common mistakes” you don’t mention which I see quite frequently. I think they both stem from thinking in imperial and therefore seeing the kilometre as a “metric mile” and a centimetre as a “metric inch” etc.
    1. Use only one prefix for any measure. “1.2 m”, not “1 m 20 cm”
    2. Use the prefixes; don’t use enormous numbers, especially if you're not using the base unit. e.g. the distance to the sun is 150 Gm, not 150,000,000 km.

  4. Martin Clutterbuck says:

    An excellent guide from the UKMA.

    It must have been hard to condense the contents of the BIPM brochure into an easy to read and handy sized document but this is a great effort, congratulations to all who created it.

    Now for the hardest part though. Getting it to the places where it will have the desired impact. This will be the next challenge!

    For my part, I will have a copy pinned to my office wall and I will encourage as many other people as possible to do the same!

  5. Erithacus says:

    @ John

    Thanks for these constructive comments, which we can consider if/when there is a second edition.

    However, we did think about most of the points that you made, and we made our judgements based on our primary objective - which is to try to influence the way the media use (and misuse) metric units. Sometimes the best is the enemy of the good.

    Responding to some of your specific points (using your numbering):

    1. In practice you rarely see l (unprefixed) but it is common as in ml, so it would have been wrong to omit it.

    2. I am afraid that bar and millibar are very well established in the UK media (and on tyre pressure gauges at petrol filling stations). You rarely see hectopascals and I think journalists' eyes would glaze over.

    3. We had particularly in mind headlines in narrow newspaper columns. Elsewhere, there usually is space, so the qualification would not apply.

    5. Inclusion of "Celsius" implies that there is a valid alternative scale. We would rather reinforce the assumption that "degrees" means "degrees Celsius." There is also a problem that some publications can't or won't use the degree symbol.

    6. m/s is actually quite useful if you want to calculate how long before you hit the bank of fog - which is what the example was about.

    7. Noted. Wasn't aware of this one, and sorry we missed it.

  6. Bob says:

    A great summary. Succinct and convenient. Thank you.

  7. John Frewen-Lord says:

    This is a truly excellent document, and I agree with the comments of all those who have responded so far. It is a sad reflection on education standards that, even among professional writers, the level of knowledge of how to 'write metric' is so abysmally poor.

    A year or so ago, there was an article in the Sunday Times (a newspaper that surely upholds the highest standards of English), which used 'kph' extensively, to the point I became very incensed over it. I wrote a letter to the editor, chastising the newspaper's solecism on the use of this incorrect symbol. The letter was published, but with an editor's comment that the Oxford English Dictionary used kph as an abbreviation for kilometres per hour, and if it was good enough for the OED, it was good enough for the ST. I checked my copy of the OED, and sure enough, under K, there is the entry: k.p.h. - abbr. for kilometres per hour.

    If the OED gets it wrong, and the ST gets it wrong, then how can we persaude the general public that the UKMA Style Guide is correct?

  8. Keith Atkin says:

    (i) L rather than l should be encouraged for the litre.
    (ii) kWh should be kW h (i.e. a space is needed to indicate multiplication).
    (iii) The use of the kW h should be discouraged and the joule and its multiples used instead. I feel particularly strongly about this as people often do not appreciate the difference between energy and power. e.g. we see the kW h (energy) being sloppily replaced by kW (power) which of course is wrong. This error is commonly seen in adverts for domestic solar heating systems.
    (iv) I am glad to see that the centimetre has not been deprecated; this unit has a clear use in many walks of life. The blanket ban on the centimetre in favour of the millimetre was, I think, the only point of disagreement I had with that wonderful man Pat Naughtin, now sadly deceased.

  9. Martin Clutterbuck says:

    Regarding the space between quantity and unit symbol, I recently had an e-mail correspondence with the editor of a technical magazine that included a mention of this BIPM specification.

    His reply was: "The thing about no space is that the number and the letter won't get separated on a line break - one needs vigilant proof reading to guard against that if there is a space! "

    He was unaware of the availability of a non-breaking space as suggested by John Steele and this may be the reason that the space is not commonly used. The character can be included in a Microsoft Word document by selecting Ctrl+Shift+Space.

  10. Erithacus says:

    @ John Frewen-Lord
    We shall of course be writing to the OED, but they will say that the OED merely records usage, and is not prescriptive. The editor of the technical journal was wrong to regard the OED as a source of authority.

  11. John Steele says:

    @John Frewen-Lord

    On kph vs. km/h, give good reference. The final paragraph of section 5.1 of the SI Brochure (I'm actually using NIST SP330) says, "It is not permissible to use abbreviations for unit symbols or unit names, such as . . ." It then goes on to illustrate improper examples. It does not mention kph explicitly but explicitly rejects mps for either m/s or metre per second.

    However, I am locked in an equally hopeless battle with the Associated Press Stylebook. As the 2012 edition has just been published and did not correct any of the seven metric errors I brought to their attention (with references), I am not making much progress. The use of kph is the dominant metric error in American media.

  12. Erithacus says:

    @ Martin C
    I am aware of the problems of persuading editors to accept the BIPM ruling on the space between number and symbol. Our task is to persuade writers that the space aids clarity and brings symbols into conformity with ordinary prose. You don't run words together, so why run numbers and symbols together - e.g. we don't write fiftygrams, so why write 50g? You are right about the non-breaking space, and it is a pity we missed the ALT + 0160 shortcut. It may be possible to amend the online download to reflect this point, but obviously the printed version cannot now be changed.

  13. Martin Clutterbuck says:

    @ John Steele

    re "The use of kph is the dominant metric error in American media."

    The international CNN channel consistently use kph for wind speed on their weather reports. I have e-mailed them with a link to the NIST style guide and the BIPM brochure suggesting that they may be interested in changing to use of the correct symbol but also with no success.

    What is the point of a country being a signatory to the BIPM and then have their 'authorities' (Associated Press, CNN, UK DfT, etc.) then ignore the standards?

  14. John Steele says:


    About 15 months ago I got the National Hurricane Center to change from an incorrect KM/HR to KM/H in their public advisory for the 2011 hurricane season (they use an all-caps Teletype format so they can't do the correct lower case). I sent the announcement to CNN and AP in hopes they would change their weather reports, but they didn't. Weather Underground on the other hand uses NHC advisories "as written" but correct the case.

    You just have to keep butting your head into the wall, and someday, it will surprise you and fall down.

  15. WJG says:

    Well done UKMA. A well thought out guide, that is clear and should be understood by all readers. I do have three comments.
    1)..L should be the preferred symbol for the litre rather than l.
    Regarding prefixes. I would have liked to have seen, the following comments added to the guide.
    2)..SI prefixes bind to a unit stronger than any mathematical operator, that is 1 km² means a kilometre squared (as in 1 (km)²) and not one kilosquaremeter (as in 1 k(m²))
    3)..SI prefixes are not allowed to be used on anything other than an unprefixed unit, in other words there is no such thing as a megakilometre or a kilosquaremetre.
    A very good guide, but the task is only half done. The guide needs to be publicised and ditributed to the printed media, schools, and general public etc.

  16. Blaise F Egan says:

    Congratulations on a good product.

    The only thing that puzzled me was the reference to not necessarily having to leave a space between number and unit, only "where there is room" . The explanation given here at Metric Views is unconvincing. Editors don't routinely write 5miles to remove the problem of lack of room, so there's no need to have 5km instead of 5 km.

    I also think we should take a stance on the l versus L issue for litres. The use of L was suggested by the USA, who are not exactly in the forefront of metrication! It is a very good idea to have one symbol instead of two and L is much better than l, which looks very much like the digit 1.

  17. Erithacus says:

    With reference to various comments on the symbol for the litre, this is the current position of CGPM:

    "The 16th Conférence Générale des Poids et Mesures (CGPM),

    recognizing the general principles adopted for writing the unit symbols in Resolution 7 of the 9th CGPM (1948),

    considering that the symbol l for the unit litre was adopted by the Comité International des Poids et Mesures (CIPM) in 1879 and confirmed in the same Resolution of 1948,

    considering also that, in order to avoid the risk of confusion between the letter l and the number 1, several countries have adopted the symbol L instead of l for the unit litre,

    considering that the name litre, although not included in the Système International d'Unités, must be admitted for general use with the System,

    decides, as an exception, to adopt the two symbols l and L as symbols to be used for the unit litre,

    considering further that in the future only one of these two symbols should be retained,

    invites the CIPM to follow the development of the use of these two symbols and to give the 18th CGPM its opinion as to the possibility of suppressing one of them.

    Comptes Rendus de la 16e CGPM (1979), 1980, 101
    Metrologia, 1980, 16(1), 56-57


    The CIPM, in 1990, considered that it was still too early to choose a single symbol for the litre."

    This remains the position in 2012.


  18. John Steele says:


    As a result of what you posted, I think both "l" and "L" have be described as "acceptable." That does not prevent a sovereign state (or a group) from designating one as preferred and the other as merely acceptable. The US has done so, preferring "L" in SP330. NIST specifically shows "L" in the table and relegates the "l vs L" to a footnote of the table. That is not to say you have to take the same stand, but there is precedence for taking a stand. The only question is whether you prefer "L". I do think the practice of using "L" alone, but "l" in "ml" is horrible and adds confusion, not clarity. Any given document should use only one form for consistency.

  19. Bob says:

    Minor issue: The style guide contains the headings "Some common units" and "Basic rules". They're misaligned vertically. The phrase "Basic units" is vertically in the middle of the cell whereas the phrase "Some common units" is just below the middle.

    The coloured backgrounds have very small misalignments. The background to "Basic units" is slightly larger vertically than the block to the left. The backgrounds to "Plurals" and "Other points" are also displaced vertically when compared with the ones to the left. There's a misaligned crossroads junction of four blocks just between "Which units to use?" and "Symbols and abbreviations".

    All very minor. I just thought I'd mention it so it can be considered if a second edition is ever published.

    [Thanks, Bob - Noted - Editor]

  20. John Steele says:

    While we are quoting the SI Brochure, I believe section 5.3.3 should be noted regarding the space between numeric value and unit:
    5.3.3 Formatting the value of a quantity
    The numerical value always precedes the unit, and a space is always used to separate the unit from the number. Thus the value of the quantity is the product of the number and the unit, the space being regarded as a multiplication sign (just as a space between units implies multiplication). The only exceptions to this rule are for the unit symbols for degree, minute, and second for plane angle, °, ', and ", respectively, for which no space is left between the numerical value and the unit symbol.

    With the use of the word "always" (and "only exception") there is no dispensation for overcrowding and I don't believe UKMA should offer a dispensation that does not, in fact, exist in the SI Brochure. The newspapers are quite capable of inventing bad practice on their own without help from metric advocates. The problem of the line breaking at this space can be solved with the non-breaking space. (there is also an html code for this symbol, although I generally use the ALT codes).

    Most newspapers either have an internal stylebook or use one such as that published by the Associated Press. You may wish to explicitly recommend the SI Brochure as a reference for their stylebook so they have an authoritative reference on SI usage. I did so with AP (recommending instead NIST SP330, the US version), although I must admit they completely ignored that and six other recommendations to correct their SI errors.

  21. Erithacus says:

    @ John and Blaise

    Please refer to the fifth comment above, bullet points 1 and 3, and also bear in mind that we are trying to offer practical help to writers - rather than just reprinting the SI brochure.

  22. Wild Bill says:

    Folks - though the comments here may be true enough, you're going to p*ss people off and make them totally refuse to use metric at all if you're going to argue the toss about every use of whitespace and whether or not the it should be "£600/kg" or "600 £/kg".

    Who cares? They're both "right enough". I'd suggest the UKMA (especially) aims for public goodwill rather than nitpicking, and tries to stop really rubbish practice like "KM" for "km", "KG" for "kg" or "kph" for "km/h" from ever gaining traction.

    Runningimp’s catalogue is an example of bad practice - it is downloadable from

    Page 12 shows that you can also get signs saying “Only 400M to go” (and similar) which is just as bad a gaffe. I took my local council to task for such an error in the local fun run last year, only to be politely told that they’d just bought the signs from Runningimp.

    May I quickly point out by the way, that Runningimp’s signs are well made, and appear to be using good tough materials and if it wasn’t for the technical errors they’d be perfect. Also Runningimp would do custom-made signs for you, saying the *right* thing if you requested it. They do nice banners and all the paraphernalia that an event organiser could ever want, and from what I’ve seen of it -it all looks great.

    It’s just that their off-the-shelf distance signs say the wrong thing. I did write to them about it last year IIRC. They’ve evidently not done anything about it. This is a new 2012 catalogue.

    These people supply signage for fun runs and cross-countries. As can be seen from their catalogue page (linked above) they have no clue how to do signs in metric despite most fun runs and probably almost all cross-countries being run in metric distances these days.

    Suppliers like these are subtly influencing the public. They should be your #1 target.

    (Editor - I am sending Running Imp a printed copy of the measurement units style guide. Let's see if this brings is an improvement to the catalogue.)


  23. philh says:

    I would like to congratulate the author(s) of the style guide. I think it is wholly appropriate for its intended audience.

    There may be shades of opinion among the "experts" here on some of the finer points but if writers follow the guide they won't go far wrong. It would certainly be a big improvement over what we typically see at present.

    I very much hope that anyone looking for such guidance make full use of this publication.

  24. M says:

    Any journalist or writer wishing to follow the advice of this Style Guide, but is lacking a suitable source to cite in order to justify reducing or ending the use of obsolete imperial units, need look no further than a recent Government statement that was made acknowledging that the understanding of imperial measurements amongst the public is so poor that they are considering adding the subject to the National Curriculum.

    The formal teaching of imperial measurements in schools was phased out over a period of years and ended completely in 1974.


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