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.

Punctuating abbreviations

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:

Ph.D. B.A. U.S.
Dr. Dept.  

But in British English it is often omitted:

Dr Dept  

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:

Fe Cu Au

And units:

m s g
kg km mm
Hz Pa W


You should be consistent throughout your text in how you space each abbreviation, for example:

6 mm
10 kg
pH 7

100 °C (temperature)
360° (angle)

Computer help

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

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:

  Singular Plural
page p. pp.
line l. ll.
following p. or l. f. ff.
manuscript ms. or MS mss. or MSS
species sp. spp.


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:

Cambridge, Mass.
San Francisco, CA
Washington, D.C.

If you add state abbreviations, be consistent in whether you use the shorter zip codes or the longer abbreviations.

State Zip Code Abbreviation
Alabama AL Ala.
Alaska AK  
Arizona AZ Ariz.
Arkansas AR Ark.
California CA Cal. or Calif.
Colorado CO Colo.
Connecticut CT Conn.
Delaware DE Del.
District of Columbia DC D.C.
Florida FL Fla.
Georgia GA Ga.
Hawaii HI  
Idaho ID  
Illinois IL Ill.
Indiana IN Ind.
Iowa IA Ia.
Kansas KS Kan. or Kans.
Kentucky KY Ky.
Louisiana LA La.
Maine ME Me.
Maryland MD Md.
Massachusetts MA Mass.
Michigan MI Mich.
Minnesota MN Minn.
Mississippi MS Miss.
Missouri MO Mo.
Montana MT Mont.
Nebraska NE Neb. or Nebr.
Nevada NV Nev.
New Hampshire NH N.H.
New Jersey NJ N.J.
New Mexico NM N. Mex. or N.M.
New York NY N.Y.
North Carolina NC N.C.
North Dakota ND N. Dak. or N.D.
Ohio OH  
Oklahoma OK Okla.
Oregon OR Ore. or Oreg.
Pennsylvania PA Pa. or Penn.
Rhode Island RI R.I.
South Carolina SC S.C.
South Dakota SD S. Dak.
Tennessee TN Tenn.
Texas TX Tex.
Utah UT Ut.
Vermont VT Vt.
Virginia VA Va.
Washington WA Wash.
West Virginia WV W. Va.
Wisconsin WI Wis. or Wisc.
Wyoming WY Wyo. or Wy.

Canadian province abbreviations

Similarly for abbreviations of Canadian provinces:

Province Postal Code Abbreviation
Alberta AB Alta.
British Columbia BC B.C.
Manitoba MB Man.
New Brunswick NB N.B.
Newfoundland and Labrador NL N.L.
Nova Scotia NS N.S.
Northwest Territories NT N.W.T.
Nunavut NU  
Ontario ON Ont.
Prince Edward Island PE P.E.I.
Quebec QC Que.
Saskatchewan SK Sask.
Yukon YT Y.T.

It is less common to add counties, states or provinces for other countries.