Abbreviations should be defined the first time they are used or in a table of abbreviations at the beginning or end of your text. Clear definitions help readers understand your writing: cross-disciplinary comprehension is important, and even standard abbreviations may not be clear to readers outside your immediate field, in another (sub)discipline or to lay readers. Abbreviations in tables and figures should also be defined, for example in a legend at the foot of the table or figure.
The rules for punctuating abbreviations are to some extent arbitrary, and vary somewhat between British and US English. It is therefore best to use your computer spelling checker or a single dictionary for consistency and, as always, follow any guidelines for publication. A number of general principles are given below.
Full stop (GB) or period (US)
On the whole, US English uses more punctuation with abbreviations than British English. For example, in US English a period is often used in:
But in British English it is often omitted:
Some US authorities, including Merriam-Webster and the Council of Science Editors, also recommend forms without a full stop or period in some cases.
In both British and US English, full stops or periods are often omitted in acronyms, i.e. words made of letters from a longer name or title:
As well as elements:
You should be consistent throughout your text in how you space each abbreviation, for example:
100 °C (temperature)
To prevent spaced units from being split from their number at the end of a line in Microsoft Word, use a nonbreaking space: Ctrl + Shift + space.
Plural abbreviations are normally written without an apostrophe:
Various NGOs were represented at the meeting.
MPs voted to increase their pay.
Interviewees included a number of CEOs.
However, do not make plurals of SI units:
|Incorrect||50 cms||90 kgs|
|Correct||50 cm||90 kg|
As already noted, the plural of a small number of abbreviations common in university and research writing is formed by doubling the final letter:
|following p. or l.||f.||ff.|
|manuscript||ms. or MS||mss. or MSS|
Use an apostrophe for the possessive form of an abbreviation:
The UN’s problems have been well documented.
The BBC’s coverage was widely praised.
MEPs’ expenses have recently come under scrutiny.
US state abbreviations
As stated above, in university and research writing US state abbreviations are often given in references to publishers or manufacturers of equipment. For example:
San Francisco, CA
If you add state abbreviations, be consistent in whether you use the shorter zip codes or the longer abbreviations.
|California||CA||Cal. or Calif.|
|District of Columbia||DC||D.C.|
|Kansas||KS||Kan. or Kans.|
|Nebraska||NE||Neb. or Nebr.|
|New Mexico||NM||N. Mex. or N.M.|
|North Dakota||ND||N. Dak. or N.D.|
|Oregon||OR||Ore. or Oreg.|
|Pennsylvania||PA||Pa. or Penn.|
|South Dakota||SD||S. Dak.|
|West Virginia||WV||W. Va.|
|Wisconsin||WI||Wis. or Wisc.|
|Wyoming||WY||Wyo. or Wy.|
Canadian province abbreviations
Similarly for abbreviations of Canadian provinces:
|Newfoundland and Labrador||NL||N.L.|
|Prince Edward Island||PE||P.E.I.|
It is less common to add counties, states or provinces for other countries.