US state abbreviations and when to use them
4 min read · 2026-03-03
Two codes, two jobs
The United States runs on two abbreviation systems: the two-letter USPS codes (CA, TX, NY) built for mail sorting, and the older AP/compact styles used in prose. For address lines and form fields, USPS codes are the default — they are unambiguous, fixed-width and machine-friendly.
Full state names still matter in UI: dropdowns, invoices and confirmation emails usually spell out "California" because humans read those surfaces, not sorting machines.
Practical rules for forms
Store the code, display the name. A
Accept both on input. If a field is free-text, normalize uppercase and match against both lists before rejecting.
Don't forget DC
The District of Columbia is not a state but has USPS code DC and appears in virtually every state list. Test suites that only iterate over the 50 states will miss forms that break on DC — a nice edge case to automate.