Use the United States Post Office’s Look Up a ZIP Code tool to look up a ZIP+4 code. Enter the full address. You can also type a ZIP+4 code into the box to find an address in the format used by the USPS.
During World War II, the Post Office started using postal district or zone numbers in big cities. It added the two-letter state abbreviations and the five-digit ZIP code in 1963 so that addresses with ZIP codes could still fit on magazine mailing labels. For second and third class mail, the USPS started requiring abbreviations and ZIP codes in 1967.
The ZIP+4 codes were made by the USPS in 1983. At first, people were against it, and in 1983, the postal service gave discounts to people who sent a lot of mail. But there was so much pushback from the public that the USPS doesn’t make people use the extra four digits.
Even though adding the last four digits usually means a single mailbox, there are some exceptions. As of 2015, the USPS uses a digital optical scanner that reads the address and prints an 11-digit bar code on each piece of mail that points to a specific mail delivery point. Nine of the 11 digits are for the ZIP+4 code, and the other two are for the delivery point.