Dealing with abbreviations, acronyms, and initialisms

August 19, 2013

Based on a writing tip I recently sent to my work colleagues.

NOTE: These are the rules based on our style guide and its referenced authorities. Your style guide may differ.


In accordance with [our style guide]:

  • Always write out in full any abbreviation/acronym/initialism (see Notes for the differences) the first time you use it in the main body of the document, then put the abbreviation in parentheses; e.g. Materials Offloading Facility (MOF). Exception: Do not write out in full common abbreviated measurement units (e.g. km).
  • After that first instance, you can use the abbreviation etc. (e.g. MOF) throughout the rest of the document, except in the References list (see Other Guidance below).


  • Don’t use punctuation between the letters of an acronym or initialism (e.g. CSIRO, not C.S.I.R.O.).
  • If the term is only used once or twice in the document, you probably don’t need to abbreviate it, unless you know your readers are more familiar with the abbreviation (e.g. GPS, PPE), in which case write it in full the first time with its abbreviation even if it’s only used once in the document.
  • If a term is used more than about five times in the document AND there’s an abbreviation for it, consider replacing the term with the abbreviation. But first consider your audience (e.g. some regulatory documents may want certain terms written in full every time).
  • If the term and abbreviation are first used inside parentheses (such as in a citation), then use square brackets for the abbreviation within the parentheses; e.g. ‘blah blah (Department of Environment and Conservation [DEC] 2007) blah blah’.
  • In the References list, write out the abbreviation etc. in full where it’s the authoring body or the publisher (e.g. ‘Department of Sustainability, Environment, Water, Population and Communities. 2012.’ not ‘SEWPaC. 2012.’)
  • Make sure all abbreviations etc. you use in the document are listed and defined in the Terms list. You still have to write each term in full the first time it’s used in the main body of the document.
  • If the term is capitalised (capped) because it’s the proper name of something (e.g. Materials Offloading Facility), then keep those capitals in the full version, but if the term is normally not capped (e.g. personal protective equipment), then only use caps in the abbreviation (e.g. PPE).
  • Follow the guidance for SI units for the abbreviation and capitalisation of units of measure; e.g. km/h not km/hr (see  http://www1.bipm.org/utils/en/pdf/si-brochure.pdf [especially the tables in Sections 2.1.2, 2.2.1, 2.2.2, and 4.1 of that document]).

NOTES (from http://grammar.quickanddirtytips.com/acronyms-grammar.aspx):

  • Initialisms are made from the first letter (or letters) of a string of words, but can’t be pronounced as words themselves. Examples include FBI, CIA, FYI (for your information), and PR (public relations).
  • Acronyms are made from the first letter (or letters) of a string of words but are pronounced as if they were words themselves. Examples include NASA, NIMBY (not in my backyard), and hazmat (hazardous materials).
  • Abbreviations are any shortened form of a word.



  1. Thank you for a timely and very helpful explanation. One small query. Is there any authority or standardised protocol for expressing the plural of acronyms/ initialisms or abbreviations. ie CEO referring to several could be CEOs or one CEO’s possessions could be CEO’s several CEOs’ possessions could be CEOs’. Common practice seems to ignore plural altogether and to infer singular, multiple or possessive status from context. Is there any advice you can give on this matter?

  2. Hi Vern

    The plural form of an abbreviation NEVER takes an apostrophe — so the plural of CEO is CEOs.

    However, the possessive form takes an apostrophe, so if something belongs to the CEO, then it’s the CEO’s possession.

    If multiple CEOs (i.e. plural CEOs) possess something, then you use the rule you would normally use for plural possessives. For example, if you were talking about the bones belonging to many dogs, you’d use the dogs’ bones. Therefore, if something belongs to multiple CEOs, you’d use CEOs’ possessions.

    Clear as mud? ;-)


  3. What convention do you follow when writing out initialisms or acronyms that start with a vowel sound? To use one of your examples one would refer to ‘a’ Materials Offloading Facility. In written form do you use ‘a’ MOB or ‘an’ MOB?

    My understanding from Fowlers is that the abbreviation should be treated as if it were pronounced, that is using ‘an’ where there is an initial vowel sound.

  4. Hi Steve

    Fortunately for us, there’s only one MOF, so we use ‘the MOF’ ;-)

    However, it’s an interesting question. I would go with how the abbreviation was pronounced and add an ‘a’ or ‘an’ appropriately.

    But the caveat there is that pronunciations differ for the same term. I’ve worked with SAP and half the people I worked with pronounced it ‘sap’ and the other half pronounced it ‘ess-ay-pee’; same for SQL — some pronounce it ‘ess-cue-ell’ while others pronounce it ‘sequel’. Even Microsoft has a bet each way on SQL. In their Manual of Style (4th edition, p388), they say to pronounce it ‘sequel’ when referring to the product name, but ‘ess-cue-ell’ when referring to ‘Structured Query Language’. They explicitly state that the latter takes the ‘an’ article, so it’s ‘an SQL database’, and for the product variation, they say to never refer to the product as ‘a SQL Server’ but instead to use ‘a computer running SQL Server’.


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