Most countries assign mailing or postal codes to areas within their cities as a means of sorting and delivering mail. The United States calls them ZIP codes. Other countries, such as Canada and Great Britain, call them postal codes. International mail uses country codes to designate the countries themselves. If you are sending something through international mail, you'll need both codes to constitute a complete address and ensure that your package reaches its intended recipient.
To send mail from outside the United States to a U.S. address, you need at least the street number and name, the ZIP code and the country code, which is US. Most cities around the world are divided into ZIP codes or the equivalent. A notable exception is Hong Kong, which is devoid of such help in finding a specific address.
Finding Postal and ZIP Codes
The United States Postal Service website has a feature for finding postal codes. Type in the full mailing address, either residential or business, and press Enter to get the ZIP code for that address. If you enter just the city and state, you'll get all ZIP codes for that city. The postal service site also provides a reverse look-up function: If you know the ZIP code but don't know where it's assigned, enter the code and the system will return the city where it is active.
Canada Post has a similar function on its site. Enter the address in the boxes provided and the system will return the postal code assigned to that address. A reverse look-up function lets you enter the postal code for a display of multiple addresses to which that code is assigned.
Great Britain's Royal Mail website allows you to start your search with either an address or a postal code using the same entry box. Entered addresses provide postal codes and entered postal codes yield multiple choices of address. The Royal Mail site allows you to change the language to Welsh for searching addresses with Welsh variants. The site limits searches in any language to 50 a day.
Sources of Other International Postal Codes
The Universal Postal Union website lists postal codes for its 191 member countries. At the UPU home page, click on a country and you're taken to an information box with a link to the official postal entity for that country and a link to its search function.
For example, if you click on Australia, you will go to the Australia Post website, where you enter the name of a suburb, city or town to find its postal code or enter the postal code for a reverse look-up. Clicking on United States takes you to the United States Postal Service search function, and clicking on Great Britain takes you to the Royal Mail's search function.
Geonames.org provides a look-up function for 63 countries. Click on the country name to see a map of the country, usually sectioned off into states or provinces. On any country's page, enter either a postal code or a city. A city search returns a range of postal codes assigned to that city. Click on any of the postal codes and you'll see a satellite view of the area with corresponding geographic labels. You may switch to map view and/or turn off the labels.
The International Standards Organization assigns the official two-letter code that identifies each country for international mail. The ISO's online browsing platform provides the code for every country with an assigned code. For reference purposes the site also lists codes that the ISO hasn't assigned.
Countrycode.org provides both the country code for international telephone calling and the ISO country code for international mail.