The Zone Improvement Plan Code (ZIP Code) is a sequence of five or nine digits developed by the United States Postal Service (USPS) to streamline the sorting and delivery of mail. Introduced in 1963, the system identifies specific geographical regions and delivery areas. The five-digit code is the foundation, with the first digit designating a broad region and subsequent digits narrowing the location to a specific sectional center facility and local delivery zone. This numerical identifier is how automated sorting machines route mail from its origin to its final destination.
Recipient and Return Address Placement
Proper address placement is dictated by the requirements of USPS automated mail processing equipment. The recipient’s address must be centered on the front face of the envelope, positioned in the lower-middle portion (generally between 5/8 inch and 2-3/4 inches from the bottom edge). All address lines should maintain a uniform left margin for optimal readability by optical character recognition (OCR) scanners.
The return address, which indicates the sender, must be placed in the upper left-hand corner. This separate placement ensures that if the mail is undeliverable, OCR technology can quickly identify the sender and route the item back. The ZIP Code placement rules apply specifically to the recipient address block, as this data drives the forward movement of the mailpiece.
The Final Line: City, State, and ZIP Code Sequence
The five-digit ZIP Code must be on the final line of the recipient’s address block. This line must follow a strict, three-part sequence: the City name, the two-letter State abbreviation, and the five-digit ZIP Code. The city and state are separated by a comma and a single space, and the state is separated from the ZIP Code by a single space (e.g., “CITY, ST 12345”).
This specific formatting and spacing are non-negotiable for high-speed sorting machines to accurately read and process the mail. To further enhance machine readability, the USPS recommends using all capital letters, omitting all punctuation marks (except the hyphen in ZIP+4), and using a clear, non-script font. Following this standardized structure allows the OCR equipment to instantly determine the correct delivery point.
Using ZIP+4 for Faster Delivery
In 1983, the USPS introduced the ZIP+4 code to provide greater precision for mail sorting. This nine-digit code includes the standard five-digit ZIP Code followed by a hyphen and four additional digits. These four digits identify a specific geographic segment within the five-digit area, such as a city block, a group of apartments, or a high-volume commercial building.
Including the ZIP+4 code helps the postal system route mail to a more specific carrier route or segment, reducing manual handling. While this extra detail is not mandatory for general delivery, it aids in faster processing and delivery. Avoid common errors like placing the ZIP Code on a separate line or using an incorrect two-letter state abbreviation, as these issues slow down or misdirect mail.