ZIP+4 codes are extensions to original five digit zip codes that include more specific geographic locations. They are designed to aid in the sorting and delivery of mail.
As of 2015, ZIP codes can be looked up at USPS.com, UnitedStatesZIPCodes.org and ZIPcode.org. All three websites offer search tools to find ZIP codes for a given location.
Non-mandatory ZIP codes were introduced to the United States in 1963. Robert Moon, a postal inspector with the United States Postal Service, proposed the ZIP code system as early as 1944.
Several websites, including Yellowpages.com, Manta.com and MerchantCircle.com, provide online search tools for locating businesses by ZIP code. To find businesses by ZIP code using these search tools, enter the ZIP code and additional information about the business into the search boxes.
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.
A list of ZIP codes is available at UnitedStatesZIPCodes.org, which provides full lists of ZIP codes for each state in the United States. Types of ZIP codes listed include standard, PO boxes, military and single-address ZIP codes.
The difference between normal ZIP codes and ZIP+4 codes is that ZIP+4 codes contain four extra digits that more accurately define the delivery area. The extra digits are not required, but they do help in routing mail more efficiently.
ZIP codes can be found at USPS.com, ZIPInfo.com and UnitedStatesZIPCodes.org, as of 2015. All three websites prompt users to enter an address to find the ZIP code.
As all ZIP codes in the United States have five digits, U.S. ZIP codes range from 00000 to 99999. One example of a notable ZIP code is 20505 for the Washington, DC CIA office, which due to high mailing volume, is uniquely used for that one address.
The United States Postal Service has a search portal that shows towns where post offices are located. Enter the ZIP code, restrict the search area to one or five miles, and then press or click "Search."