What are a country’s ISO, phone and domain codes?

How it works

Every country and many territories have three codes in the international standard ISO 3166-1: two letters (FI), three letters (FIN) and three digits (246). Forms, passports, shipping labels and software use them so that a country never depends on its name in one language. The digits are the same as the United Nations’ M49 codes, so they also work where the Latin alphabet doesn’t.

Telephone calling codes come from a different standard, ITU-T E.164, and don’t follow countries one to one: +1 is shared by the United States, Canada and much of the Caribbean, which are told apart by a three-digit area code (+1 684 is American Samoa), and +44 covers the United Kingdom and the Crown Dependencies. To call Finland from abroad you dial the exit prefix of the country you are in (00 in most of Europe, 011 from North America), then 358, then the number without its trunk prefix: 040 123 4567 becomes +358 40 123 4567.

Internet country domains mostly reuse the two-letter code (.fi, .de), with one well-known exception: the United Kingdom is GB in ISO 3166 but uses .uk. The codes change rarely, when a country is created or renamed; dialling rules change more often. The sources and the date we last checked them are listed under the table.

Aircraft carry yet another code. Under ICAO Annex 7 every registration begins with the nationality mark of the state of registry, taken from that country’s ITU radio call sign series: OH- for Finland, G- for the United Kingdom, D- for Germany, and N for the United States, which writes no hyphen. The longest mark that fits wins, so B-HNR is Hong Kong while plain B- is shared by China and Taiwan. The mark tells you the register, not the owner or where the aircraft flies.