The United States Postal Service introduced the Zone Improvement Plan (ZIP) in 1963 for more efficient mail delivery. Addressing a letter without it could lengthen delivery time or cause the mail carrier to return it to you. If you don't know the ZIP code for an address, you can use one of several online resources to find it. Most are free unless you require additional services.
USPS Zip Lookup
The USPS provides a ZIP code search tool on its website. You can get to it from the homepage when you click on "Quick Tools" and select "Look Up a ZIP code" from the drop-down menu. Enter the street address, city and state in the appropriate boxes and click on the "Find" button. The tool displays the ZIP code and its four-number extension on the following page.
Melissa Data is a database containing all U.S. addresses in the format the USPS uses. You can locate a ZIP code using the ZIP code lookup tool. Click "Lookups" on the main page. On the next page, choose "Address Check" under the "Address and Street Data" column. The following page provides two methods of entering the address. You can type the address into the Express Entry box or copy it from your source document and paste it into the text box. Click the submit button to view results.
Whitepages is an online database of contact information in North America that lets you search for other people with known addresses. Bear in mind that this option only works as long as the person's information is in the system. Navigate to the website at Whitepages.com. From there, enter the name, city and state of the person whose ZIP code you need. The results page will display any matching names. If you locate the right person, click on "address" and his address and ZIP code will show up. If his name does not appear -- or, for someone with a common name, you can't find the specific person you are searching for -- you won't get his address or ZIP code information on this site.
Mapping websites such as Mapquest, Google Map and Yahoo Maps display addresses on a map and generate directions from starting to ending points. These sites also provide suggestions for incorrect addresses and fill in missing details, such as the ZIP code. For example, on the Mapquest home page you can type the address into the search field and click the "search" button. The address will come up along with the ZIP code.