NumberGlossaryCountry Code
International (ITU-T E.164); +1 = North American Numbering Plan · also called country calling code, international dialing code, E.164 country code, +1
The ITU-T E.164 dialing prefix that identifies a country or integrated numbering plan; +1 covers the entire North American Numbering Plan.
A country code (formally a "country calling code") is the prefix defined by ITU-T Recommendation E.164 that identifies a country, a set of countries sharing an integrated numbering plan, or a particular geographic or global service area, so that a call can be routed internationally. The code +1 is not the code for the United States alone: it is the single country code shared by the whole North American Numbering Plan (NANP), covering the US, Canada, and roughly 18 other Caribbean and North Atlantic countries and territories — about 25 numbering regions across 20 countries — each distinguished only by its own three-digit area code (NPA).
Country codes are assigned and published by the ITU under E.164 and range from one to three digits. E.164 caps the total international number at 15 digits including the country code, so the digits available for the national number equal 15 minus the length of the country code. Because +1 is only one digit, a full NANP number is written +1 followed by the 10-digit domestic number (NPA-NXX-line) — the 10-digit national number sits directly under the shared +1 code.
+1 does not mean "United States." It is a shared country code used by every NANP member — Canada, and roughly 18 Caribbean and North Atlantic nations and territories, in addition to the US. A number beginning +1 tells you the NANP, not which specific country; the following three-digit area code (NPA) is what identifies the region.