When Did State Abbreviations Transition to All Capital Letters?
The use of two-letter postal abbreviations in all capital letters for U.S. states was standardized by the United States Postal Service (USPS) in 1963. Prior to this change, state abbreviations varied and included a mix of capital and lowercase letters. This change was implemented to create a uniform system that would be easily recognizable and suitable for machine sorting and processing of mail.
Standardization in 1963
To Eric Chiaramonte
The all-caps format for state abbreviations was officially announced by the USPS in October 1963. This standardization of state abbreviations was designed for the ease and efficiency of mail delivery, particularly with the introduction of five-digit ZIP codes.
States with identical initials were assigned unique abbreviations to avoid confusion. For example, Massachusetts (MA), Maryland (MD), Michigan (MI), Minnesota (MN), Missouri (MO), Mississippi (MS), and Montana (MT) all adopt all-capital abbreviations. This change made the abbreviations more distinct for machines to process, but less intuitive for humans to read.
Technical Reasons and Machine Readability
The all-caps format in state abbreviations was primarily to accommodate the limitations on the length of address lines when adding the five-digit ZIP code. Additionally, it ensured that each state could be easily and uniquely identified without ambiguity, especially in an era before digital address scanning.
Usage in Documentation and Media
However, the all-capital two-letter state abbreviations are not typically used in documents, books, newspapers, and other media meant for human readers. Humans are more accustomed to seeing abbreviated state names like "Calif." for "California" rather than the more machine-friendly "CA." The Chicago Manual of Style, the Associated Press (AP) Stylebook, and other style guides provide guidelines for state abbreviations that are more readable and sensible to humans.
Conclusion
The transition to all-capital state abbreviations occurred in 1963 as part of USPS's efforts to standardize postal systems and improve mail delivery efficiency. However, this standardization primarily applies to official USPS documents and forms. For general use in written communication and media, other abbreviations remain more intuitive and widely accepted by the public.