State Abbreviations

There are three different ways to write state names: you can spell them out in their entirety, you can use traditional abbreviations, or you can use postal abbreviations. In most cases, postal abbreviations are appropriate and well understood. There are situations, however, in which it's correct to spell out state names. The decision will depend on the context of your writing and on the style guide you're following.

When to Spell Out State Names

As a general rule, the names of states should be spelled out when they appear in sentences but abbreviated in other contexts. For example:

• "Our family had been transferred from Endicott, New York, to Raleigh, North Carolina. That was the word used by the people at IBM, transferred." (David Sedaris, "Naked," 1997)
• "Both men were raised in the Midwest (Garfield in Ohio, Guiteau in Illinois) by a single, widowed parent." (Sarah Vowell, "Assassination Vacation," 2005)

This rule applies also if you are writing something formal and following a style guide, such as the Chicago Manual of Style, MLA Style, American Psychological Association Publication Manual (APA), or Associated Press Style (AP). 

When to Use State Abbreviations

In bibliographies, lists, charts where space is at a premium, reference lists, footnotes and endnotes, and in mailing addresses, state names are usually shortened using the postal abbreviation. This applies to Chicago Manual of Style and the American psychological Association Style (APA).

The two-letter, no-period state abbreviations recommended by the U.S. Postal Service (see "Postal Abbreviations" in the chart below) should always be used where a Zone Improvement Plan (ZIP) code follows. These postal abbreviations may also be used in any context where abbreviations are appropriate.

Some writers and editors still prefer to use the older forms of state abbreviations (see "Traditional Abbreviations in the table below), though this is rare.  In 1987, the Secretary of Commerce switched to the more commonly used two-letter postal code abbreviations. If you follow the older practice, be consistent in your use of the traditional abbreviations, and remember that eight states (Alaska, Hawaii, Idaho, Iowa, Maine, Ohio, Texas, and Utah) are only rarely abbreviated when using the older (pre-ZIP code) forms.

Why the ZIP Code Abbreviations Were Developed

Before 1963, there were no ZIP codes used on postal mail in the United States, and the U.S. Post Office preferred that people wrote out state and territory names completely to avoid confusion in sorting mail. In the early 1800s, it had established a standardized list of acceptable abbreviations, updating it in 1874. The list remained relatively unchanged until ZIP codes were introduced. 

The addition of seven additional characters on a final address line (ZIP code plus two spaces) necessitated the shortening of state abbreviations to fewer characters. The Post Office aimed to fit the final address line into 23 characters to accommodate "major addressing systems."

U.S. or US for United States

Finally, United States may be abbreviated to U.S. when used as an adjective, but in formal writing, it's customarily spelled out as a noun. If you are following the Chicago Manual, you'll remove the periods to become US except in bibliography or reference entries pertaining to U.S. statutes, court cases, and other legal-context usages, which retain the periods. If you're following APA or AP, you will keep the periods there too. MLA prefers to spell out United States as an adjective or a noun in running text.

List of State Abbreviations

This handy chart has both the postal and the traditional abbreviations, for your reference: