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I remember reading somewhere that if a unit is abbreviated as one character, there must not be a space between the number and the unit (e.g., 5m, 26K). If the unit is abbreviated as two or more Characters, there must be a space between the number and the unit (e.g., "10 km", "USD 5").

  • Can you please help me find the source again?
  • Is this recommendation correct?
apaderno
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Vaibhav Garg
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    Nitpick: you probably meant "10 km" (if it's about kilometres) – Jonik Sep 11 '10 at 17:52
  • I suggest that would have no use, even if you could explain it in detail.

    Are you really suggesting we should use 5m but 12 km? How could anyone justify that?

    Why not just use either SI units, or your own publisher's house style?

     – Robbie Goodwin Apr 25 '20 at 21:32

3 Answers3

70

If you're typesetting SI units, it seems logical to follow the conventions of the Bureau international des poids et mesures. From the SI Brochure, §5.3.3:

The numerical value always precedes the unit, and a space is always used to separate the unit from the number. (…) 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.

§5.3.7 goes on to say that “When it is used, a space separates the number and the symbol %.”

In practice, it is quite common to see non-alphabetic units such as % and °C typeset without an intervening space. I've never seen a rule that distinguished between single-letter units and longer units.

Note that the rule doesn't specify how wide the space should be. Some references recommend a normal inter-word space, while others recommend a thin space. In any case, the space is nonbreakable.

These rules need not apply to currencies, especially when they are written before the number. Specifying that single-character currencies don't take a space ($42, £42, €42) while multiple-character currencies do (AUD 42, A$ 42) doesn't feel completely outlandish, maybe that's what you remember?

Pete Kirkham
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Gilles 'SO- stop being evil'
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  • Fully agreed (especially about omitting the space before % and °C being common, even if non-conforming). SI specifies a thin space for thousands separation (if used) and just says space between number and unit, so I guess it would always be a normal (non-breaking) space. • The Euro is customarily written after the number: 12.34 € (with a non-breaking space) – mirabilos Jan 11 '19 at 17:30
  • @mirabilos In English € is usually written before the number. I think that's true in all English-speaking countries. In most of the Eurozone the symbol comes after the number and a non-breaking space, but this site is about English. – Gilles 'SO- stop being evil' Jan 11 '19 at 18:05
  • @mirabilos SI does not specify a thin space for thousands separation. This was a mistake by the English translator which was fixed in the meanwhile. In this answer, I write: "SI wants to prescribe the presence of spaces at certain positions, but not their exact width" – mhchem Sep 10 '20 at 16:51
  • Ah okay, so it was updated in 2019. As I don’t speak French I cannot comment further (but I do remember looking up the English text of the spec a while ago). – mirabilos Sep 10 '20 at 16:55
  • List of exceptions to the rule are incomplete. There are other instances such as using K or M etc. as shorthand for thousands and millions. E.g. 10K, 1.5M, etc. Consider also other symbolic units such as cubic meters (㎥), inches ("), litres (ℓ), etc. when do these have spaces and when do they not? –  Sep 07 '21 at 08:30
  • @JoelKarunungan My answer is mostly about typesetting SI units, such as ㎥, L (ℓ is a non-standard notation). For those, the SI rules state a nonbreakable space, but individual publications may adopt other rules. Inches " and feet ' follow the same rules as when these notations are used for arc minutes and seconds: no space. For most non-SI units, there is no widely applicable standard, so it's a matter of individual taste or individual publication's typesetting rules. – Gilles 'SO- stop being evil' Sep 07 '21 at 10:04
  • As a side note, the currency unit in the European countries I know is written after the value, usually with the abbreviation/symbol (i.e 12€ or 12 zł, as opposed to €12 or 12 PLN). The exception is the UK (£12) – WoJ Sep 07 '22 at 08:37
  • @WoJ In most European countries, when writing in the native language, the currency symbol comes after the number. But that has no relevance to English. Both English-speaking countries in the Eurozone (Ireland and Malta) write the currency first AFAIK. – Gilles 'SO- stop being evil' Sep 07 '22 at 17:41
  • @Gilles'SO-stopbeingevil': you are right, but for one the discussion spawned SI rules and then English is the basic communication language between people not speaking a common one. I am French, and when writing in English to a German friend I will not write "it costs €3" but "it costs 3€" because this is the way we both use units. – WoJ Sep 08 '22 at 07:58
  • Good answer indeed, one remark: % is not a unit, BIPM defines it as "parts per hundred", and NIST indicates "% is used to represent simply the number 0.01". – mins Apr 30 '23 at 15:31
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In Canadian Style: A Guide to Writing and Editing:

  • When symbols are used, the prefix symbol and unit symbols are run
    together:

    5 cm
7 hL
4 dag
13 kPa

  • When a symbol consists entirely of letters, leave a full space between
    the quantity and the symbol:

    45 kg not 45kg

  • When the symbol includes a non-letter character as well as letter, leave no space:

    32°C not 32° C or 32 °C

However, the International System of Units, or SI, requires a space to be used to separate the unit symbol from the numerical value, and this also applies to the symbol for the degree Celsius, as 32 °C. The only exceptions to this rule in the SI are for the symbols for degree, minute and second for plane angle, as 30° 22′ 8″. Wikipedia's style guide also follows the SI standard.

  • For the sake of clarity, a hyphen may be inserted between a numeral and a symbol used adjectivally:

    35-mm film
60-W bulb

However, some other style guides, including Wikipedia's, deprecate hyphenation in these cases. The SI allows a hyphen between the numeral and the unit only when the name of the unit is spelled out, as 35-millimetre film.

Source: https://en.wikipedia.org/wiki/Space_%28punctuation%29#Unit_symbols_and_numbers

Community
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b.roth
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3

Addressing the OP's second question and setting currencies aside, the answer may be that both are 'correct' as long as you are consistent.

This may be an example of where everyday usage is at variance with style guides. I'm sure that most academic papers will follow the advice of number + space + measurement, but if you do an image search for food labels for example, they seem to almost invariably omit the space between the number and the weight. E.g. '200g' and not '200 g', and 'Fat: 8%' rather than 'Fat: 8 %'. This may simply be due to space being at a premium on a label, but I suspect it's more widespread than that.

This is not to say that the style guides are 'wrong' but may suggest that it's now widely acceptable to omit the space and that perhaps the convention is changing over time. A quick search for '200g' vs '200 g' using Google's Ngram viewer suggests that the usage of measurement without the space may have caught up with or even overtaken 'number + space + g' over the last two decades.

T. Ioca
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