Look at any envelope with an American address. After the city comes a two-letter code, like TX or NY, then the ZIP Code. Those are postal codes.
Key idea
Every state has a two-letter postal code, written in capital letters with no period: CA for California, TX for Texas, NY for New York. D.C. is DC.
Why it works
Why two letters? In 1963 the Post Office brought in five-digit ZIP Codes. The machines that printed addresses could fit only about 23 characters on the last line, so long state names had to shrink. The Post Office gave every state a two-letter code that no other state shares. (Nebraska was NB at first; it became NE in 1969 so it would not be confused with New Brunswick in Canada.)
Worked example: The M states
Eight states start with M. What are their codes?
- Maine ME, Maryland MD, Massachusetts MA.
- Michigan MI, Minnesota MN.
- Mississippi MS, Missouri MO, Montana MT.
- Notice that only MA, MI and MO follow a simple rule; the rest use a later letter.
Answer: ME, MD, MA, MI, MN, MS, MO, MT.
Common mistake
Guessing from the first two letters goes wrong for states that share a start. AK is Alaska and AR is Arkansas (AL is Alabama, AZ is Arizona). IA is Iowa, ID Idaho, IL Illinois, IN Indiana. MI is Michigan, not Mississippi (MS) or Missouri (MO). Learn the look-alikes as a group.
| Starts with | Codes |
|---|---|
| A | AL Alabama, AK Alaska, AZ Arizona, AR Arkansas |
| I | ID Idaho, IL Illinois, IN Indiana, IA Iowa |
| N | NE Nebraska, NV Nevada, NH New Hampshire, NJ New Jersey, NM New Mexico, NY New York, NC North Carolina, ND North Dakota |
| W | WA Washington, WV West Virginia, WI Wisconsin, WY Wyoming |