In order to find the postal code for a specific address within the United States, online visitors to the United States Postal Service website can use the Look Up a ZIP Code web tool. It is accessed through the Quick Tools tab in the menu bar at USPS.com.
In the United States, postal codes, also known as ZIP codes, allow the United States Postal Service to determine the geographic location and delivery route associated with a particular address. Each digit or group of digits within the ZIP code indicate the USPS location that is responsible for handling the delivery of mail to that address.
The first digit identifies the state or group of states to which the address belongs. The second and third digits identify the distribution service center, and the last two digits indicate the specific post office that is responsible for the delivery of mail to the address. Additionally, mail may be addressed by the use of a "ZIP +4". A ZIP +4 contains an additional four digits, which allows the post office to determine the city block or specific recipient. While using a ZIP +4 is not mandatory, as of 2015, it can help ensure faster processing and delivery.