The United State Postal Service provides links to find ZIP codes on its website, USPS.com. As of 2015, UnitedStatesZIPCode.org and ZIPCode.org provide ZIP code search tools as well.
To find a ZIP code on the USPS website, navigate to USPS.com, and click on Look Up a ZIP Code. Enter the street address and city, and select the state. The nine-digit ZIP code is then displayed for the given address. The USPS site also has a reverse lookup tool that displays a list of cities within a given ZIP code.
UnitedStatesZIPCode.org has an address search bar and a reverse ZIP code lookup tool on its homepage and displays a regional map of the searched ZIP code area. To find a ZIP code on ZIPCode.org, select ZIP Code Search on its homepage.