What is ZIP+4?
The four extra digits after the dash narrow a ZIP code down to a small delivery segment.
A standard ZIP code has five digits and covers an area served by one post office or delivery unit. The USPS introduced ZIP+4 in 1983. The extra four digits identify a much smaller group of addresses: a side of a city block, a floor of a large building, a single high-volume business, or a range of PO boxes.
How to read a ZIP+4
- First digit: a group of states (0 in the Northeast up to 9 on the West Coast).
- Next two digits: a regional sorting center (sectional center facility).
- Last two of the five: the local post office or delivery area.
- +4, first two: the delivery sector.
- +4, last two: the delivery segment (for example one side of a block).
Do I need it?
No. Mail with a correct 5-digit ZIP is delivered. ZIP+4 helps automated sorting, and many business systems and forms ask for it.